Multiprocessing and Multithreading

[Chandru Rajendran]

Hi all,

Please give me an idea about Multiprocessing and Multithreading.

Thanks & Regards,
Chandru

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Re for Apache log file format

[Sam Giraffe]

Hi,

I am trying to split up the re pattern for Apache log file format and seem
to be having some trouble in getting Python to understand multi-line
pattern:

#!/usr/bin/python

import re

#this is a single line
string = '192.168.122.3 - - [29/Sep/2013:03:52:33 -0700] "GET / HTTP/1.0"
302 276 "-" "check_http/v1.4.16 (nagios-plugins 1.4.16)"'

#trying to break up the pattern match for easy to read code
pattern = re.compile(r'(?P\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})\s+'
 r'(?P\-)\s+'
 r'(?P\-)\s+'
 r'(?P\[(.*?)\])\s+'
 r'(?P\"(.*?)\")\s+'
 r'(?P\d{3})\s+'
 r'(?P\d+)\s+'
 r'(?P\"\")\s+'
 r'(?P\((.*?)\))')

match = re.search(pattern, string)

if match:
print match.group('ip')
else:
print 'not found'

The python interpreter is skipping to the 'math = re.search' and then the
'if' statement right after it looks at the , instead of moving onto
 and so on.

mybox:~ user$ python -m pdb /Users/user/Documents/Python/apache.py
> /Users/user/Documents/Python/apache.py(3)()
-> import re
(Pdb) n
> /Users/user/Documents/Python/apache.py(5)()
-> string = '192.168.122.3 - - [29/Sep/2013:03:52:33 -0700] "GET /
HTTP/1.0" 302 276 "-" "check_http/v1.4.16 (nagios-plugins 1.4.16)"'
(Pdb) n
> /Users/user/Documents/Python/apache.py(7)()
-> pattern = re.compile(r'(?P\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})\s+'
(Pdb) n
> /Users/user/Documents/Python/apache.py(17)()
-> match = re.search(pattern, string)
(Pdb)

Thank you.
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Re: Code golf challenge: XKCD 936 passwords

[Steve Simmons]

Chris Angelico  wrote:
>On Tue, Oct 8, 2013 at 5:48 PM,   wrote:
>> And if we were actually trying then that filename should just be
>"/w". Would get rid of another 19 chars.
>
>I'm working this on the assumption that the dictionary file already
>exists (that's where it is on my Debian Linux systems, for instance)
>and shouldn't be moved :)
>
>ChrisA
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Typical MUD Master - making up rules as you go along :-)

Sent from a Galaxy far far away-- 
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Re: Code golf challenge: XKCD 936 passwords

[Chris Angelico]

On Tue, Oct 8, 2013 at 6:02 PM, Steve Simmons  wrote:
> Typical MUD Master - making up rules as you go along :-)

Totally. Under the auspices of Rule Zero:
http://tvtropes.org/pmwiki/pmwiki.php/Main/RuleOfFun

:)

ChrisA
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Re: Tail recursion to while iteration in 2 easy steps

[Jussi Piitulainen]

random...@fastmail.us writes:

> The entire point of tail call optimization requires not keeping the
> intervening stack frames around, in _any_ form, so as to allow
> arbitrarily deep recursion without ever having the possibility of a
> stack overflow. An implementation which reduced but did not
> eliminate the space used per call would not be worthwhile because it
> would not enable the recursive functional programming patterns that
> mandatory tail call optimization allows.
> 
> You could require that an "optimizable tail call" be made explicit.
> Actually, I suspect it might be possible to do this now, by abusing
> exception handling as a control flow mechanism.

Python code already marks many of the functionally relevant tail calls
with 'return'. It just wants to retain the trace.

Another keyword could be used to indicate that the programmer does not
want a stack frame retained. It's probably too much to suggest 'please
return', but how about 'goto return'?

A tail call is a 'goto that passes arguments', and I think 'goto' is a
keyword already.

(Actually I just wanted to suggest 'please return'. Not seriously.)
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Re: Multiprocessing and Multithreading

[Terry Reedy]

On 10/8/2013 1:34 AM, Chandru Rajendran wrote:


Please give me an idea about Multiprocessing and Multithreading.


Please give us some idea of what you know and what you actually want to 
know.



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And please try to avoid this bulky disclaimer that is a lie.

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Re: Multiprocessing and Multithreading

[Mark Lawrence]

On 08/10/2013 06:34, Chandru Rajendran wrote:

Hi all,

Please give me an idea about Multiprocessing and Multithreading.

Thanks & Regards,

Chandru



I'll assume that you're a newbie so I'll keep it simple. 
Multiprocessing is about more than one process and multithreading is 
about more than one thread.  If you want Python specifics you could 
start here http://docs.python.org/3/library/multiprocessing.html or here 
http://docs.python.org/3/library/threading.html, both of which may have 
been found by using your favourite search engine.


--
Roses are red,
Violets are blue,
Most poems rhyme,
But this one doesn't.

Mark Lawrence

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Re: Tail recursion to while iteration in 2 easy steps

[Jussi Piitulainen]

Steven D'Aprano writes:

> Far more useful would be a high-level description of Scheme's
> programming model. If names can be rebound on the fly, how does
> Scheme even tell whether something is a recursive call or not?
> 
> def foo(arg):
> do stuff here
> foo(arg-1)  # how does Scheme know that this is the same foo?

In general, it doesn't know. It just calls whatever function is bound
to foo. It does know that the call is in a tail position.

If the compiler has access to all code that can possibly change the
value of foo, it can know simply by proving that there is no such
assignment statement in the code. This can happen if the compiler is
told to assume that it has the whole program. It often happens in a
local scope. Module systems create such local scopes for unexported
variables, and even for exported variables by forbidding assignments
outside.

(I'm not sure if your question was rhetorical or if you were looking
for this information.)
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Re: Code golf challenge: XKCD 936 passwords

[Mark Lawrence]

On 08/10/2013 07:48, sprucebond...@gmail.com wrote:

On Monday, October 7, 2013 8:45:39 PM UTC-10, spruce...@gmail.com wrote:

On Monday, October 7, 2013 8:17:21 PM UTC-10, Chris Angelico wrote:


Who's up for some fun? Implement an XKCD-936-compliant password
generator in Python 3, in less code than this:
print(*__import__("random").sample(open("/usr/share/dict/words").read().split("\n"),4))



Second challenge: Use it for generating all your passwords :)



[1] https://en.wikipedia.org/wiki/Code_golf
[2] http://xkcd.com/936/



ChrisA


Well, here's a start:

import random as r
print(*r.sample(open("/usr/share/dict/words").readlines(),4))
Shaves off 6 characters.


And if we were actually trying then that filename should just be "/w". Would 
get rid of another 19 chars.



Very impressive, you've saved a total of 25 characters on one line and 
added too many lines to count to your emails, which I've snipped. 
Please read and digest this 
https://wiki.python.org/moin/GoogleGroupsPython, thanks in anticipation.


--
Roses are red,
Violets are blue,
Most poems rhyme,
But this one doesn't.

Mark Lawrence

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Re: Formal-ity and the Church-Turing thesis

[Steven D'Aprano]

On Tue, 08 Oct 2013 10:46:50 +0530, Ravi Sahni wrote:

> On Tue, Oct 8, 2013 at 8:47 AM, rusi  wrote:
>> I can only say how ironic it sounds to someone who is familiar with the
>> history of our field: Turing was not a computer scientist (the term did
>> not exist then) but a mathematician.  And his major contribution was to
>> create a form of argument so much more rigorous than what erstwhile
>> mathematicians were used to that he was justified in calling that math
>> as a machine.
>>
>> The irony is that today's generation assumes that 'some-machine'
>> implies its something like 'Intel-machine'. To get out of this
>> confusion ask yourself: Is it finite or infinite? If the TM were finite
>> it would be a DFA If the Intel-machine (and like) were infinite they
>> would need to exist in a different universe.
> 
> With due respect Sir, you saying that Turing machine not a machine? Very
> confusion Sir!!!

The mathematical ideal Turing Machine has an infinitely long tape, 
equivalent to infinite memory, and may take an unbounded amount of time 
to complete the computation. Since no *actual* physical machine can be 
infinitely big, and in practice there are strict limits on how long we 
are willing to wait for a computation to complete, in the *literal* 
sense, Turing Machines are not *actual* machines. They are a mathematical 
abstraction.

But in practice, we can wave our hands and ignore this fact, and consider 
only not-quite-Turing Machines with finite amounts of tape, and note that 
they are equivalent to physical machines with finite amounts of memory. 
One could even build such a finite Turing Machine, although of course it 
would be very slow. Or one can simulate it in software.

So in that sense, computers are Turing Machines. Anything a physical 
computing device can compute, a Turing Machine could too. The converse is 
not true though: a Turing Machine with infinite tape can compute things 
where a real physical device would run out of memory, although it might 
take longer than anyone is willing to wait.



-- 
Steven
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Re: HEX to ASCII

[markotaht]

esmaspäev, 7. oktoober 2013 18:52.21 UTC+3 kirjutas Piet van Oostrum:
> markot...@gmail.com writes:
> 
> 
> 
> > This is the code i came up with:
> 
> > from teisendaja import *
> 
> > from operator import *
> 
> > import binascii
> 
> >
> 
> > teisendus = teisendus()
> 
> > kood = input("Kood: ")
> 
> > key = input("Võti: ")
> 
> >
> 
> > chunksize = 2
> 
> > vastus = [teisendus.teisendus3(16,2,kood[i: (i + chunksize)]) for i in 
> > range(0, len(kood),chunksize)]
> 
> > vastus = ["0"*(8-len(x)) + x for x in vastus]
> 
> > #key = teisendus.teisendus3(10,2,int(key))
> 
> > getBin = lambda x, n: x >= 0 and str(bin(x))[2:].zfill(n) or "-" + 
> > str(bin(x))[3:].zfill(n)
> 
> 
> 
> Instead of boolean and expr1 or expr2 in current Python you can better write:
> 
> expr1 if boolean else expr2.
> 
> and I think using def getBin(x, n):would be more clear. 
> 
> 
> 
> But I have another observation: You use getBin only for positive ints, so the 
> whole '-' case isn't necessary. Actually it would be damaging, as the rest of 
> the code assumes that the key that results from getBin is 8 characters long, 
> whereas in the negative case it would be 9 characters. Also you use 
> int(key[j]) and if key[0] == '-' this would give an error.
> 
> If you just want to get 8 binary digits for an int using format would be 
> simpler:
> 
> 
> 
> getBin = lambda x, n: '{0:={1}b}'.format(x, n)
> 
> or getBin = lambda x, n: '{0:=0{1}b}'.format(x, n) if you want also negatives 
> (but this would give you 7 or eight binary digits, not always 8.)
> 
> 
> 
> 
> 
> > def dekrüpteeria(vastus, key):
> 
> > XOR = []
> 
> > tulemus = []
> 
> > for i in range(len(vastus)):
> 
> > for j in range(8):
> 
> > XOR.append(str(ixor(int(vastus[i][j]), int(key[j]
> 
> > tulemus.append("".join(XOR))
> 
> > key = "".join(XOR)
> 
> > XOR = []
> 
> > return tulemus
> 
> 
> 
> You can use list comprehension:
> 
> 
> 
> def dekrüpteeria(vastus, key):
> 
> tulemus = []
> 
> for i in range(len(vastus)):
> 
> XOR = [(str(ixor(int(vastus[i][j]), int(key[j] for j in range(8)]
> 
> tulemus.append("".join(XOR))
> 
> key = "".join(XOR)
> 
> return tulemus
> 
> 
> 
> and then because you only use "".join(XOR), not XOR itself:
> 
> 
> 
> def dekrüpteeria(vastus, key):
> 
> tulemus = []
> 
> for i in range(len(vastus)):
> 
> XOR = "".join([(str(ixor(int(vastus[i][j]), int(key[j] for j in 
> range(8)])
> 
> tulemus.append(XOR))
> 
> key = XOR
> 
> return tulemus
> 
> 
> 
> and then you could rewrite this also to use a list comprehension for tulemus, 
> but that may make it in a too big one liner.
> 
> 
> 
> Also note that you always use int() on the elements of key and vastus, so it 
> might be simpler to store these as int arrays (lists) instead of strings
> 
> >
> 
> > tulemus2= []
> 
> > if key == "":
> 
> > for i in range(256):
> 
> > võti = getBin(i,8)
> 
> > tulemus = [teisendus.teisendus3(2,16,i) for i in 
> > dekrüpteeria(vastus, võti)]
> 
> > tulemus = ["0"*(2-len(x)) + x for x in tulemus]
> 
> 
> 
> Look at the zfill method for the above 2 line
> 
> 
> 
> Probably
> 
> tulemus = [teisendus.teisendus3(2,16,i).zfill(2) for i in 
> dekrüpteeria(vastus, võti)]
> 
> will do the same
> 
> 
> 
> ># for j in range(len(tulemus)):
> 
> > tulemus2.append(binascii.unhexlify("".join(tulemus)))
> 
> > print("Key-" + str(võti) + ": " + str(tulemus2))
> 
> > tulemus2 = []
> 
> > #tulemus = [teisendus.teisendus3(2,16,i) for i in dekrüpteeria(vastus, key)]
> 
> > #print(":".join(tulemus))
> 
> >
> 
> > #751a6f1d3d5c3241365321016c05620a7e5e34413246660461412e5a2e412c49254a24
> 
> >
> 
> > Although this is quite ugly atm. But it serves me well, until i reach the 
> > unhexlify part. The number and lette r string at the wery end is the mesage 
> > im trying to decypher. 
> 
> 
> 
> The result of unhexlify is a byte string. So tulemus2 is a list of byte 
> strings, which you can joint with xxx = b''.join(tulemus2), and then you have 
> another byte string. If you are sure this is ASCII (which means all bytes are 
> < 128), the you can convert it to a string with str(xxx, 'ascii') or 
> xxx.decode('ascii'). If there are bytes > 127 then you have to know which 
> encoding it is to be able to make a string out of it.
> 
> 
> 
> Is this some known encryption method? If so why not use a standard solution 
> for it? If it is a home brew encryption: are you sure it is safe? Most home 
> brew solutions in encryption are not.
> 
> -- 
> 
> Piet van Oostrum 
> 
> WWW: http://pietvanoostrum.com/
> 
> PGP key: [8DAE142BE17999


Are you familira with the page called hacker.org? THere are tons of challenges. 
And this is one of the cypher challenges called Feedback cypher. The end result 
should be in the format of "The antswer is ." Or something like that. The 
problem is that the

Re: HEX to ASCII

[markotaht]

esmaspäev, 7. oktoober 2013 17:16.29 UTC+3 kirjutas Mark Lawrence:
> On 07/10/2013 14:54, markot...@gmail.com wrote:
> 
> > I forgot to tell. The teisendaja module that i have imported, is a number 
> > converter that allow to convert numbers from one base to another. i mostly 
> > use it for HEX to BIN and vice versa, but it supports other bases too.
> 
> >
> 
> 
> 
> That's nice to know, but what has it got to do with the market price of 
> 
> oranges in Timbuktu?  Or to put it another way, you're forcing 
> 
> volunteers to go and find your original message as once again you don't 
> 
> quote any context.  Please make life easier for everybody, including 
> 
> yourself, by quoting something from the original.
> 
> 
> 
> Thanks in anticipation.
> 
> 
> 
> -- 
> 
> Roses are red,
> 
> Violets are blue,
> 
> Most poems rhyme,
> 
> But this one doesn't.
> 
> 
> 
> Mark Lawrence
teisendaja module doesent matter. Only thing that matters about is that it 
returns a string with the converted number.
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Re: class implementation

[markotaht]

I cant just subclassing doesent work. It seem the init method of the source 
class also calls out another class. And the problem is, i can subclass the 
other class to with the required function but the end result is that it doesent 
work, since the source class cant accsess the subclass functions. 

The source code is pykkar. 

https://courses.cs.ut.ee/all/MTAT.03.100/2012_fall/uploads/opik/_downloads/pykkar.py

I want to add it a new ability called left(). I cant manipulate the source 
class, cause then my comp will be the only one where the program runs.

class pykkar_l(Pykkar):
def left(self):
self._world.execute("left")

def _cmd_left(self):
headings = (N,E,S,W)
cur_tile = self._get_current_tile() 

cur_heading_index = headings.index(cur_tile.pykkar_heading)
new_heading_index = (cur_heading_index - 1) % 4
cur_tile.pykkar_heading = headings[new_heading_index]

self._update_pykkar_image(cur_tile)

class world_l(World):
def left(self):
self._world.execute("left")

These are my subclasses. For it to work. Class World, must obtain the method 
from subclass world_l
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Re: HEX to ASCII

[Mark Lawrence]

On 08/10/2013 09:13, markot...@gmail.com wrote:

esmaspäev, 7. oktoober 2013 17:16.29 UTC+3 kirjutas Mark Lawrence:

On 07/10/2013 14:54, markot...@gmail.com wrote:


I forgot to tell. The teisendaja module that i have imported, is a number 
converter that allow to convert numbers from one base to another. i mostly use 
it for HEX to BIN and vice versa, but it supports other bases too.


That's nice to know, but what has it got to do with the market price of
oranges in Timbuktu?  Or to put it another way, you're forcing
volunteers to go and find your original message as once again you don't
quote any context.  Please make life easier for everybody, including
yourself, by quoting something from the original.
Thanks in anticipation.

--

Roses are red,
Violets are blue,
Most poems rhyme,
But this one doesn't.
Mark Lawrence

teisendaja module doesent matter. Only thing that matters about is that it 
returns a string with the converted number.



Actually another thing that matters is finding a technology that doesn't 
spread superfluous newlines throughout emails.  I've snipped them above. 
 Please take note of this 
https://wiki.python.org/moin/GoogleGroupsPython.  Thanks in aniticipation.


--
Roses are red,
Violets are blue,
Most poems rhyme,
But this one doesn't.

Mark Lawrence

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Re: Variable arguments (*args, **kwargs): seeking elegance

[Peter Cacioppi]

On Saturday, October 5, 2013 9:04:25 PM UTC-7, John Ladasky wrote:
> Hi folks,
> 
> 
> 
> I'm trying to make some of Python class definitions behave like the ones I 
> find in professional packages, such as Matplotlib.  A Matplotlib class can 
> often have a very large number of arguments -- some of which may be optional, 
> some of which will assume default values if the user does not override them, 
> etc.
> 
> 
> 
> I have working code which does this kind of thing.  I define required 
> arguments and their default values as a class attribute, in an OrderedDict, 
> so that I can match up defaults, in order, with *args.  I'm using 
> set.issuperset() to see if an argument passed in **kwargs conflicts with one 
> which was passed in *args.  I use  set.isdisjoint() to look for arguments in 
> **kwargs which are not expected by the class definition, raising an error if 
> such arguments are found.
> 
> 
> 
> Even though my code works, I'm finding it to be a bit clunky.  And now, I'm 
> writing a new class which has subclasses, and so actually keeps the "extra" 
> kwargs instead of raising an error... This is causing me to re-evaluate my 
> original code.
> 
> 
> 
> It also leads me to ask: is there a CLEAN and BROADLY-APPLICABLE way for 
> handling the *args/**kwargs/default values shuffle that I can study?  Or is 
> this sort of thing too idiosyncratic for there to be a general method?
> 
> 
> 
> Thanks for any pointers!

"One thought -- often, people turn to subclassing as the only tool in
their toolbox. Have you considered that it may be easier/better to work
with delegation and composition instead? "

Double like.

Subclassing is awesome when it is used properly ... which usually means used 
cautiously.

Delegation/composition just doesn't result in the some sort of weird gotchas.

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Re: class implementation

[Mark Lawrence]

On 08/10/2013 09:20, markot...@gmail.com wrote:

To whom and to what are you replying?

--
Roses are red,
Violets are blue,
Most poems rhyme,
But this one doesn't.

Mark Lawrence

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Re: Tail recursion to while iteration in 2 easy steps

[Alain Ketterlin]

random...@fastmail.us writes:

> On Mon, Oct 7, 2013, at 13:15, Alain Ketterlin wrote:
>> That's fine. My point was: you can't at the same time have full
>> dynamicity *and* procedural optimizations (like tail call opt).
>> Everybody should be clear about the trade-off.
>
> Let's be clear about what optimizations we are talking about. Tail call
> optimization, itself, doesn't care _what_ is being called. It can just
> as easily mean "erase its own stack frame and replace it with that of
> another function" as "reassign the arguments and jump to the top of this
> function". Some people have introduced the idea of _further_
> optimizations, transforming "near" tail recursion (i.e. return self()+1)
> into tail recursion, and _that_ depends on knowing the identity of the
> function (though arguably that could be accounted for at the cost of
> including dead code for the path that assumes it may have been changed),
> but tail call optimization itself does not.

You're right, thanks for the clarification.

-- Alain.
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Re: Tail recursion to while iteration in 2 easy steps

[Alain Ketterlin]

Antoon Pardon  writes:

> Op 07-10-13 19:15, Alain Ketterlin schreef:

[...]
>> That's fine. My point was: you can't at the same time have full
>> dynamicity *and* procedural optimizations (like tail call opt).
>> Everybody should be clear about the trade-off.
>
> Your wrong. Full dynamics is not in contradiction with tail call
> optimisation. Scheme has already done it for years. You can rebind
> names to other functions in scheme and scheme still has working
> tail call optimisatiosn.

See
http://en.wikipedia.org/wiki/Scheme_%28programming_language%29#Lexical_scope

(first sentence, about variable bindings).

-- Alain.
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Re: Tail recursion to while iteration in 2 easy steps

[Antoon Pardon]

Op 08-10-13 01:50, Steven D'Aprano schreef:
> On Mon, 07 Oct 2013 15:47:26 -0700, Mark Janssen wrote:
> 
>> I challenge you to get
>> down to the machine code in scheme and formally describe how it's doing
>> both.
> 
> For which machine?
> 
> Or are you assuming that there's only one machine code that runs on all 
> computing devices?
> 
> 
> Frankly, asking somebody to *formally* describe a machine code 
> implementation strikes me as confused. Normally formal descriptions are 
> given in terms of abstract operations, often high level operations, 
> sometimes *very* high level, and rarely in terms of low-level "flip this 
> bit, copy this byte" machine code operations. I'm not sure how one would 
> be expected to generate a formal description of a machine code 
> implementation.
> 
> But even putting that aside, even if somebody wrote such a description, 
> it would be reductionism gone mad. What possible light on the problem 
> would be shined by a long, long list of machine code operations, even if 
> written using assembly mnemonics?
> 
> Far more useful would be a high-level description of Scheme's programming 
> model. If names can be rebound on the fly, how does Scheme even tell 
> whether something is a recursive call or not?
> 
> def foo(arg):
> do stuff here
> foo(arg-1)  # how does Scheme know that this is the same foo?

It doesn't and it doesn't need to. tail call optimisation is not
limited to recursive functions. All tail calls can be optimised,
recurisive call and others.

-- 
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inserting or updating appropriately

[Νίκος Αλεξόπουλος]

Hello, i'am trying to insert a new record or update an existing one in 
case counterID(stands for the page's URL) and cookieID(random number) is 
the same:


try:
		# if first time for webpage; create new record( primary key is 
automatic, hit is defaulted ), if page exists then update record
		cur.execute('''INSERT INTO counters (url) VALUES (%s) ON DUPLICATE KEY 
UPDATE hits = hits + 1''', page )

# get the primary key value of the new added record
cID = cur.lastrowid

		# if first time visitor on this page, create new record, if visitor 
exists then update record
		cur.execute('''INSERT INTO visitors (counterID, cookieID, host, city, 
useros, browser, ref, lastvisit) VALUES (%s, %s, %s, %s, %s, %s, %s, %s)
	   ON DUPLICATE KEY UPDATE cookieID = %s, host = %s, city = %s, 
useros = %s, browser = %s, ref = %s, hits = hits + 1, lastvisit = %s

   WHERE counterID = %s and cookieID = 
%s''',
	   (cID, cookieID, host, city, useros, browser, ref, lastvisit, 
cookieID, host, city, useros, browser, ref, lastvisit, cID, cookieID) )

=

Error is: ProgrammingError(ProgrammingError(1064, "You have an error in 
your SQL syntax; check the manual that corresponds to your MySQL server 
version for the right syntax to use near 'WHERE counterID = 1 and 
cookieID = '3815'' at line 3"),)


i notticed that if i remove the WHERE clause in the last execute it 
works but then its not updating properly.


Can this happen in 1-statemnt with the ON DUPLICATE KEY INVOLVED WITHOUT 
BREAKING IT IN IN 2-STATEMNTS?


THANKS.
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Re: Tail recursion to while iteration in 2 easy steps

[Steven D'Aprano]

On Mon, 07 Oct 2013 20:27:13 -0700, Mark Janssen wrote:

 But even putting that aside, even if somebody wrote such a
 description, it would be reductionism gone mad. What possible light
 on the problem would be shined by a long, long list of machine code
 operations, even if written using assembly mnemonics?
>>>
>>> Only that you've got a consistent, stable (and therefore,
>>> formalizable) translation from your language to the machine.
>>
>> You are mistaken to think that there is a single, one-to-one, mapping
>> between high-level code and machine code.
> 
> It's not mistaken.

I'm afraid it is. Reality trumps your theory. gcc, clang, Microsoft 
Visual Studio, and all the many, many other C compilers do not generate 
identical machine code even when targeting the same hardware. This is a 
fact. It's not even the case that there is One True Way to implement a 
particular program on a given hardware device and compilers merely are 
buggy for doing something else. There are often different ways to 
implement it which are equally good, the only difference being personal 
preference.


> Given a stable and formalized language definition,
> there should only be continued optimization of the lexical and
> procedural constructs into better machine code.

Better than what? "Continued" optimization? When you say "lexical and 
procedural constructs", do you mean "source code"?


> In the case of an
> "interpreted" language like Python (which I'll define as a language
> which includes a layer of indirection between the user and the machine,

Irrelevant. In the case of Python, there is a machine. The fact that it 
is a VM rather than a physical machine is irrelevant. A machine is a 
machine -- we could be talking about a Lisp Machine, a Forth Machine, a 
x86 processor, an Motorola 68000, an Atom processor, one of those old 
Russian mainframes that used three-state trits instead of two-state bits, 
or even Babbage's Analytical Engine. 

Besides, most modern CPUs don't execute machine code directly, they run 
the machine code in a virtual machine implemented in hardware. So the 
difference between Python and x86 machine code is just a matter of degree.



> encouraging the nice benefits of interactivity), such optimization isn't
> really apropos, because it's not the purpose of python to be optimal to
> the machine as much as "optimal to the programmer".  In any case, while
> such optimization can continue over time, they generally create new
> compiler releases to indicate such changes.  The one-to-one mapping is
> held by the compiler.
> 
> Such determinism *defines* the machine, otherwise you might as well get
> rid of the notion of computer *science*.  All else is error, akin to
> cosmic rays or magic.  Unless the source code changes, all else
> remaining equal, the machine code is supposed to be the same, no matter
> how many times it is compiled.

That is akin to saying that there is *only one* way to measure the speed 
of light (say), standing in exactly the same place, using exactly the 
same equipment, using precisely the same measurement techniques, and that 
if we allow alternative methods for measuring the speed of light, physics 
is no longer a science.


>>[Only if you use the exact source, compiler, switches, etc]] will the
>>output be the same.
>> And even that is not guaranteed.
> 
> Oh, and what would cause such non-determinism?

The compiler-writer, of course. A compiler is software, and is written by 
a person, who can program it to do anything the writer wants. If the 
writer wants the compiler to be non-deterministic, it can be.

Some viruses use a similar technique to try to avoid virus scanners. They 
encrypt the payload, which is functionally equivalent to randomizing it 
(except it can be reversed if you have the key) so as to defeat virus 
scanners.

A more whimsical example: perhaps a mischievous compiler writer included 
something like this in her compiler:


when compiling integer multiplication, INT * INT:
  if today is Tuesday:
emit machine code that does multiplication using repeated addition
  otherwise:
emit machine code that does multiplication using ADD and SHIFT


Both implementations of multiplication are perfectly valid. There may be 
a performance difference, or there may not be. Since no sensible 
programming language is going to specify the *detailed* machine code 
implementation of its high-level operations, such a mischievous compiler 
would still be valid.


>> Take, for example, the single high-level operation:
>>
>> sort(alist)
>>
>> What machine code will be executed? Obviously that will depend on the
>> sort algorithm used. There are *dozens*. Here are just a few:
> 
> Well, since you didn't specify your programming language, you're then
> merely stating an English construct.

What difference does it make? But if it will make you feel better, I'm 
specifying Hypertalk. You've probably never heard of it, but regardless, 
it exists, and it has a so

Re: inserting or updating appropriately

[Νίκος Αλεξόπουλος]

Στις 8/10/2013 12:15 μμ, ο/η Νίκος Αλεξόπουλος έγραψε:

Hello, i'am trying to insert a new record or update an existing one in
case counterID(stands for the page's URL) and cookieID(random number) is
the same:

 try:
 # if first time for webpage; create new record( primary key is
automatic, hit is defaulted ), if page exists then update record
 cur.execute('''INSERT INTO counters (url) VALUES (%s) ON
DUPLICATE KEY UPDATE hits = hits + 1''', page )
 # get the primary key value of the new added record
 cID = cur.lastrowid

 # if first time visitor on this page, create new record, if
visitor exists then update record
 cur.execute('''INSERT INTO visitors (counterID, cookieID, host,
city, useros, browser, ref, lastvisit) VALUES (%s, %s, %s, %s, %s, %s,
%s, %s)
ON DUPLICATE KEY UPDATE cookieID = %s, host =
%s, city = %s, useros = %s, browser = %s, ref = %s, hits = hits + 1,
lastvisit = %s
WHERE counterID = %s and cookieID = %s''',
(cID, cookieID, host, city, useros, browser,
ref, lastvisit, cookieID, host, city, useros, browser, ref, lastvisit,
cID, cookieID) )
=

Error is: ProgrammingError(ProgrammingError(1064, "You have an error in
your SQL syntax; check the manual that corresponds to your MySQL server
version for the right syntax to use near 'WHERE counterID = 1 and
cookieID = '3815'' at line 3"),)

i notticed that if i remove the WHERE clause in the last execute it
works but then its not updating properly.

Can this happen in 1-statemnt with the ON DUPLICATE KEY INVOLVED WITHOUT
BREAKING IT IN IN 2-STATEMNTS?

THANKS.


Actually what i want is this effect in cur.execute statement:

		# if first time visitor on this page, create new record, if visitor 
exists then update record
		cur.execute('''INSERT INTO visitors (counterID, cookieID, host, city, 
useros, browser, ref, lastvisit) VALUES (%s, %s, %s, %s, %s, %s, %s, %s)''',

   (cID, cookieID, host, city, useros, 
browser, ref, lastvisit)

		cur.execute('''UPDATE visitors SET cookieID = %s, host = %s, city = 
%s, useros = %s, browser = %s, ref = %s, hits = hits + 1, lastvisit = %s

   WHERE counterID = %s and cookieID = 
%s''',
	   (cookieID, host, city, useros, browser, ref, lastvisit, cID, 
cookieID) )


--
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Re: inserting or updating appropriately

[Ben Finney]

Νίκος Αλεξόπουλος  writes:

> Error is: ProgrammingError(ProgrammingError(1064, "You have an error
> in your SQL syntax; check the manual that corresponds to your MySQL
> server version for the right syntax to use near 'WHERE counterID = 1
> and cookieID = '3815'' at line 3"),)

This is an error from the database server. It has nothing to do with
Python, as you already know from previous discussions here.

Please do not ask questions about usage of the database server here any
more.

-- 
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  `\   |
_o__)  |
Ben Finney

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Re: Tail recursion to while iteration in 2 easy steps

[Antoon Pardon]

Op 07-10-13 23:27, random...@fastmail.us schreef:
> On Sat, Oct 5, 2013, at 3:39, Antoon Pardon wrote:
>> What does this mean?
>>
>> Does it mean that a naive implementation would arbitrarily mess up
>> stack traces and he wasn't interested in investigating more
>> sophisticated implementations?
>>
>> Does it mean he just didn't like the idea a stack trace wouldn't be a
>> 100% represenatation of the active call history?
>>
>> Does it mean he investigated more sphisticated implementations but found
>> them to have serious short comings that couldn't be remedied easily?
> 
> The entire point of tail call optimization requires not keeping the
> intervening stack frames around, in _any_ form, so as to allow
> arbitrarily deep recursion without ever having the possibility of a
> stack overflow. An implementation which reduced but did not eliminate
> the space used per call would not be worthwhile because it would not
> enable the recursive functional programming patterns that mandatory tail
> call optimization allows.

So? What about an implementation that would keep its stackframes
normally until it deteced recursion had occured. From then on it
would only keep what it already had plus the four top stackframes
(assuming it are all tail calls for the moment). This would allow
for a stacktrace of the last four calls and essentially doesn't need
any space per call from then on.

-- 
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Re: Tail recursion to while iteration in 2 easy steps

[Jussi Piitulainen]

Alain Ketterlin writes:
> Antoon Pardon writes:
> 
> > Op 07-10-13 19:15, Alain Ketterlin schreef:
> 
> [...]
> >> That's fine. My point was: you can't at the same time have full
> >> dynamicity *and* procedural optimizations (like tail call opt).
> >> Everybody should be clear about the trade-off.
> >
> > Your wrong. Full dynamics is not in contradiction with tail call
> > optimisation. Scheme has already done it for years. You can rebind
> > names to other functions in scheme and scheme still has working
> > tail call optimisatiosn.
> 
> See
> http://en.wikipedia.org/wiki/Scheme_%28programming_language%29#Lexical_scope
> 
> (first sentence, about variable bindings).

# ... Scheme is lexically scoped: all possible variable bindings in a
# program unit can be analyzed by reading the text of the program unit
# without consideration of the contexts in which it may be called ...

The actual procedure to be called is still not known at compile time,
in general. It can be a parameter. It needn't even be the value of any
explicit variable (needn't be "bound to a name").

def call(f, a):
   ...
   return f(a)  # tail call
   ...

def wev(...):
   ...
   return (fs if c(k) else gs)[k](a)  # tail call
   ...

In the Scheme reports, a variable is said to be bound to a location,
which is lexically apparent to the language processor; the value is
stored in that location, and assignment to the variable means storing
a new value in that location. It works like Python or Java; Python
just has a different way of talking about how it works - binding names
directly to values in a namespace, and rebinding to different values.

However, Scheme processors know that the local variables are not
accessible from anywhere else but the local code, so there are more
opportunities for compile-time analysis. They can optimize many of
those locations away, for example.
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Cookie gets changed when hit comes from a referrer

[Νίκος Αλεξόπουλος]

# initialize cookie and retrieve cookie from clients browser
cookie = cookies.SimpleCookie( os.environ.get('HTTP_COOKIE') )

if cookie.get('ID') is not None:
cookieID = cookie['ID'].value
else:
cookieID = random.randrange(0, )
cookie['ID'] = cookieID
cookie['ID']['path'] = '/'
print( cookie )

===
===

I use this code to retrive or set a cookie to the visitor's browser if 
present and identify him bu it.


All work well except the situation where the user visits my webpage by 
clicking a backlink on another wbpage.


Then for some reason the cookieID changes to another value thus a new 
entry appears into the database when insert happens.


What cna i do about that?
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class-private names and the Zen of Python

[Marco Buttu]

In the following case:

>>> class Foo:
... _Foo__a = 100
... __a = 33
...
>>> Foo._Foo__a
33

I think this behavior, for a user who does not know the convention, 
could be a surprise. Should be raising an exception (in order to inform 
the user the transformation of the name __a have been replaced an 
existing name) a possible --explicit-- alternative?


Another question is: where is the place in which this transformation 
occurs? Is it at the parser level, before the dictionary attribute is 
gave as argument to the metaclass?


I looked at the documentation:

http://docs.python.org/3/reference/lexical_analysis.html
http://docs.python.org/3/reference/expressions.html#atom-identifiers

but it is not clear when this transformation happens.

--
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Re: Re for Apache log file format

[Andreas Perstinger]

On 08.10.2013 08:33, Sam Giraffe wrote:

#this is a single line
string = '192.168.122.3 - - [29/Sep/2013:03:52:33 -0700] "GET / HTTP/1.0"
302 276 "-" "check_http/v1.4.16 (nagios-plugins 1.4.16)"'

#trying to break up the pattern match for easy to read code
pattern = re.compile(r'(?P\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})\s+'
  r'(?P\-)\s+'
  r'(?P\-)\s+'
  r'(?P\[(.*?)\])\s+'
  r'(?P\"(.*?)\")\s+'
  r'(?P\d{3})\s+'
  r'(?P\d+)\s+'
  r'(?P\"\")\s+'
  r'(?P\((.*?)\))')


[SNIP]


The python interpreter is skipping to the 'math = re.search' and then the
'if' statement right after it looks at the , instead of moving onto
 and so on.


I'm not sure if I understand your problem, but your regex pattern only 
matches up to the size. When you look for the referrer, the pattern 
expects two quotes but in your string you have "-" (quote, dash, quote). 
Thus there is no match (i.e. "match" is None) and the if-statement will 
print "not found".


Bye, Andreas
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Re: class implementation

[Dave Angel]

On 8/10/2013 04:20, markot...@gmail.com wrote:

> I cant just subclassing doesent work.

I can't parse that "sentence."

> It seem the init method of the source class also calls out another
class. And the problem is, i can subclass the other class to with the required 
function but the end result is that it doesent work, since the source class 
cant accsess the subclass functions. 

What's a "source class"?  If you mean parent class, then say so.
Otherwise, if you give it a name, we might be able to follow.   But
"source" and "other" don't narrow the field very much.

A parent class can certainly access the child class (subclass) 
methods (not functions).  But only if the instance (self) is an instance
of the child class. That's the whole point of subclassing.

>
> The source code is pykkar. 
>
> https://courses.cs.ut.ee/all/MTAT.03.100/2012_fall/uploads/opik/_downloads/pykkar.py
>
> I want to add it a new ability called left(). I cant manipulate the source 
> class, cause then my comp will be the only one where the program runs.
>
> class pykkar_l(Pykkar):
> def left(self):
> self._world.execute("left")
>
> def _cmd_left(self):
> headings = (N,E,S,W)
> cur_tile = self._get_current_tile() 
> 
> cur_heading_index = headings.index(cur_tile.pykkar_heading)
> new_heading_index = (cur_heading_index - 1) % 4
> cur_tile.pykkar_heading = headings[new_heading_index]
> 
> self._update_pykkar_image(cur_tile)
>
> class world_l(World):
> def left(self):
> self._world.execute("left")
>
> These are my subclasses. For it to work. Class World, must obtain the method 
> from subclass world_l

Then it sounds like you should make sure that the global value "world"
in that module is an instance of your world_l class, rather than an
instance or World.  And that the proxy is an instance of pykkar_l rather
than of Pykkar.

import pykkar

layout = "fdlkjdsljdslfkjsdljfdsf"
pykkar.world = world_I(layout)
??? = pykkar_l(pykkar.world)

You don't show your own top-level code, so I can't integrate it in.

By the way, it's conventional to use uppercase for class names, and
lowercase for instances of those classes.

I'm astounded that your class is using eval and multiprocessing before
understanding classes and subclasses.


-- 
DaveA


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Re: class-private names and the Zen of Python

[Terry Reedy]

On 10/8/2013 6:13 AM, Marco Buttu wrote:

In the following case:

 >>> class Foo:
... _Foo__a = 100
... __a = 33
...
 >>> Foo._Foo__a
33

I think this behavior, for a user who does not know the convention,
could be a surprise.


No one qualified to use such names would do such a thing , so there is 
no need to worry about it or do anything about it.


--
Terry Jan Reedy

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Re: class-private names and the Zen of Python

[Marco Buttu]

On 10/08/2013 12:36 PM, Terry Reedy wrote:


On 10/8/2013 6:13 AM, Marco Buttu wrote:

In the following case:

 >>> class Foo:
... _Foo__a = 100
... __a = 33
...
 >>> Foo._Foo__a
33

I think this behavior, for a user who does not know the convention,
could be a surprise.


No one qualified to use such names would do such a thing , so there is
no need to worry about it or do anything about it.


Is this transformation performed by the parser, before to call the 
metaclass?


--
Marco Buttu
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Re: class-private names and the Zen of Python

[Ned Batchelder]

On 10/8/13 6:13 AM, Marco Buttu wrote:

In the following case:

>>> class Foo:
... _Foo__a = 100
... __a = 33
...
>>> Foo._Foo__a
33

I think this behavior, for a user who does not know the convention, 
could be a surprise. Should be raising an exception (in order to 
inform the user the transformation of the name __a have been replaced 
an existing name) a possible --explicit-- alternative? 


You also get a "problem" if you do this:

>>> class Foo:
   ... a = 100
   ... a = 33
   ...
>>> Foo.a
   33

Or for that matter:

>>> a = 100
>>> a = 33
>>> a
   33

There are lots of ways to change what value a name refers to, it's not 
an error to reassign names.


Also, as Terry mentions, no one has ever assigned the two names you 
show, so why try to warn about it?


--Ned.
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Re: Cookie gets changed when hit comes from a referrer

[Ian Kelly]

On Tue, Oct 8, 2013 at 4:04 AM, Νίκος Αλεξόπουλος  wrote:
> I use this code to retrive or set a cookie to the visitor's browser if
> present and identify him bu it.
>
> All work well except the situation where the user visits my webpage by
> clicking a backlink on another wbpage.
>
> Then for some reason the cookieID changes to another value thus a new entry
> appears into the database when insert happens.
>
> What cna i do about that?

This question is really about HTTP, not Python, so you'd have better
luck asking elsewhere.  The most likely possibility is that the domain
doesn't match.  For example, the cookie is set for the domain
www.foo.com, and the other webpage is linking to foo.com.  Another
possibility is that the cookie is expiring because the browser session
was terminated, not because of anything to do with the other webpage.
Or it could simply be a bug or unusual setting in whatever browser
you're using to test it.
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Re: class-private names and the Zen of Python

[Marco Buttu]

On 10/08/2013 01:07 PM, Ned Batchelder wrote:


On 10/8/13 6:13 AM, Marco Buttu wrote:


>>> class Foo:
... _Foo__a = 100
... __a = 33
...
>>> Foo._Foo__a
33


...

You also get a "problem" if you do this:

 >>> class Foo:
... a = 100
... a = 33
...
 >>> Foo.a
33


But this does not happen under the hood, it is explicit


Also, as Terry mentions, no one has ever assigned the two names you
show,


Sincerely, I can not now if someone has assigned (or will assegne) in 
such way...


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parsing email from stdin

[Antoon Pardon]

I want to do some postprocessing on messages from a particular mailbox.
So I use getmail which will fetch the messages and feed them to stdin
of my program.

As I don't know what encoding these messages will be in, I thought it
would be prudent to read stdin as binary data.

Using python 3.3 on a debian box I have the following code.

#!/usr/bin/python3

import sys
from email import message_from_file

sys.stdin = sys.stdin.detach()
msg = message_from_file(sys.stdin)

which gives me the following trace back

  File "/home/apardon/.getmail/verdeler", line 7, in 
msg = message_from_file(sys.stdin)
  File "/usr/lib/python3.3/email/__init__.py", line 56, in message_from_file
return Parser(*args, **kws).parse(fp)
  File "/usr/lib/python3.3/email/parser.py", line 58, in parse
feedparser.feed(data)
  File "/usr/lib/python3.3/email/feedparser.py", line 167, in feed
self._input.push(data)
  File "/usr/lib/python3.3/email/feedparser.py", line 100, in push
data, self._partial = self._partial + data, ''
TypeError: Can't convert 'bytes' object to str implicitly))

which seems to be rather odd. The following header are in the msg:

Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 8bit

So why doesn't the email parser lookup the charset and use that
for converting to string type?

What is the canonical way to parse an email message from stdin?

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Re: Code golf challenge: XKCD 936 passwords

[Roy Smith]

In article ,
 Chris Angelico  wrote:

> On Tue, Oct 8, 2013 at 5:48 PM,   wrote:
> > And if we were actually trying then that filename should just be "/w". 
> > Would get rid of another 19 chars.
> 
> I'm working this on the assumption that the dictionary file already
> exists (that's where it is on my Debian Linux systems, for instance)
> and shouldn't be moved :)
> 
> ChrisA

In the old days, it used to be /usr/dict/words.  Port Python to v6, and 
save another 6 characters :-)
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Re: Formal-ity and the Church-Turing thesis

[Ravi Sahni]

On Tue, Oct 8, 2013 at 1:20 PM, Steven D'Aprano  wrote:
> On Tue, 08 Oct 2013 10:46:50 +0530, Ravi Sahni wrote:
>
>> On Tue, Oct 8, 2013 at 8:47 AM, rusi  wrote:
>>> I can only say how ironic it sounds to someone who is familiar with the
>>> history of our field: Turing was not a computer scientist (the term did
>>> not exist then) but a mathematician.  And his major contribution was to
>>> create a form of argument so much more rigorous than what erstwhile
>>> mathematicians were used to that he was justified in calling that math
>>> as a machine.
>>>
>>> The irony is that today's generation assumes that 'some-machine'
>>> implies its something like 'Intel-machine'. To get out of this
>>> confusion ask yourself: Is it finite or infinite? If the TM were finite
>>> it would be a DFA If the Intel-machine (and like) were infinite they
>>> would need to exist in a different universe.
>>
>> With due respect Sir, you saying that Turing machine not a machine? Very
>> confusion Sir!!!
>
> The mathematical ideal Turing Machine has an infinitely long tape,
> equivalent to infinite memory, and may take an unbounded amount of time
> to complete the computation. Since no *actual* physical machine can be
> infinitely big, and in practice there are strict limits on how long we
> are willing to wait for a computation to complete, in the *literal*
> sense, Turing Machines are not *actual* machines. They are a mathematical
> abstraction.
>
> But in practice, we can wave our hands and ignore this fact, and consider
> only not-quite-Turing Machines with finite amounts of tape, and note that
> they are equivalent to physical machines with finite amounts of memory.
> One could even build such a finite Turing Machine, although of course it
> would be very slow. Or one can simulate it in software.
>
> So in that sense, computers are Turing Machines. Anything a physical
> computing device can compute, a Turing Machine could too. The converse is
> not true though: a Turing Machine with infinite tape can compute things
> where a real physical device would run out of memory, although it might
> take longer than anyone is willing to wait.

Thanks Sir the detailed explanation. You are offering me many thoughts
inside few words so I will need some time to meditate upon the same.

Presently Sir, I wish to ask single question: What you mean "wave our hands"??

Thanks
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Re: Re for Apache log file format

[Neil Cerutti]

On 2013-10-08, Sam Giraffe  wrote:
>
> Hi,
>
> I am trying to split up the re pattern for Apache log file format and seem
> to be having some trouble in getting Python to understand multi-line
> pattern:
>
> #!/usr/bin/python
>
> import re
>
> #this is a single line
> string = '192.168.122.3 - - [29/Sep/2013:03:52:33 -0700] "GET / HTTP/1.0"
> 302 276 "-" "check_http/v1.4.16 (nagios-plugins 1.4.16)"'
>
> #trying to break up the pattern match for easy to read code
> pattern = re.compile(r'(?P\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})\s+'
>  r'(?P\-)\s+'
>  r'(?P\-)\s+'
>  r'(?P\[(.*?)\])\s+'
>  r'(?P\"(.*?)\")\s+'
>  r'(?P\d{3})\s+'
>  r'(?P\d+)\s+'
>  r'(?P\"\")\s+'
>  r'(?P\((.*?)\))')

I recommend using the re.VERBOSE flag when explicating an re.
It'll make your life incrementally easier.

pattern = re.compile(
 r"""(?P\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})\s+
 (?P\-)\s+
 (?P\-)\s+
 (?P\[(.*?)\])\s+# You can even insert comments.
 (?P\"(.*?)\")\s+
 (?P\d{3})\s+
 (?P\d+)\s+
 (?P\"\")\s+
 (?P\((.*?)\))""", re.VERBOSE)

-- 
Neil Cerutti
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Re: Formal-ity and the Church-Turing thesis

[Ravi Sahni]

On Tue, Oct 8, 2013 at 11:14 AM, rusi  wrote:
> To explain at length will be too long and OT (off-topic) for this list.
> I'll just give you a link and you tell me what you make of it:
> http://sloan.stanford.edu/mousesite/Secondary/Whorfframe2.html


I am trying to read link. Very new idea: Buildings can catch fire by
wrong boards!!

Later part difficult for me to read.  (My English not powerful --please excuse.)
I will make my fullest efforts to read on your recommend but I not
clear the connection with computers, programming, computer science and
so on.  Also this Mr. Mark Lawrence question.

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Re: Formal-ity and the Church-Turing thesis

[Steven D'Aprano]

On Tue, 08 Oct 2013 18:16:01 +0530, Ravi Sahni wrote:

>> So in that sense, computers are Turing Machines. Anything a physical
>> computing device can compute, a Turing Machine could too. The converse
>> is not true though: a Turing Machine with infinite tape can compute
>> things where a real physical device would run out of memory, although
>> it might take longer than anyone is willing to wait.
> 
> Thanks Sir the detailed explanation. You are offering me many thoughts
> inside few words so I will need some time to meditate upon the same.
> 
> Presently Sir, I wish to ask single question: What you mean "wave our
> hands"??

It is an idiom very common in Australia. (It may not be well known in the 
rest of the English-speaking world.) It means to figuratively flap one's 
hands around in the air while skipping over technical details or 
complications. For example, we often talk about "hand-wavy estimates" for 
how long a job will take: "my hand-wavy estimate is it will take two 
days" is little better than a guess.


-- 
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Re: class-private names and the Zen of Python

[Steven D'Aprano]

On Tue, 08 Oct 2013 12:13:48 +0200, Marco Buttu wrote:

> In the following case:
> 
>  >>> class Foo:
> ... _Foo__a = 100
> ... __a = 33
> ...
>  >>> Foo._Foo__a
> 33
> 
> I think this behavior, for a user who does not know the convention,
> could be a surprise. 

Yes, you are correct. It surprised me, and I've been using Python for 
more than 15 years, and I know the convention of double-underscore name-
mangling.


> Should be raising an exception (in order to inform
> the user the transformation of the name __a have been replaced an
> existing name) a possible --explicit-- alternative?

No, I don't think so. That would slow down class creation, for no real 
benefit. Except for the name-mangling part, this is no different from:

class Spam:
x = 23
x = 42

If anything, something like PyLint or PyChecker could warn about it. But 
the language itself is fine like it is.


> Another question is: where is the place in which this transformation
> occurs? Is it at the parser level, before the dictionary attribute is
> gave as argument to the metaclass?

Good question!

I don't have a full answer, but I have a part answer: it occurs before 
the metaclass sees the namespace:

py> class Meta(type):
... def __new__(meta, name, bases, namespace):
... print(namespace)
... return super().__new__(meta, name, bases, namespace)
...
py>
py> class Test(metaclass=Meta):
... __test = 'foo'
...
{'__module__': '__main__', '_Test__test': 'foo', '__qualname__': 'Test'}


so I think it is done by the parser.



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Re: Formal-ity and the Church-Turing thesis

[rusi]

On Tuesday, October 8, 2013 6:31:21 PM UTC+5:30, Ravi Sahni wrote:
> On Tue, Oct 8, 2013 at 11:14 AM, rusi  wrote:
> > To explain at length will be too long and OT (off-topic) for this list.
> > I'll just give you a link and you tell me what you make of it:
> > http://sloan.stanford.edu/mousesite/Secondary/Whorfframe2.html
> 
> 
> I am trying to read link. Very new idea: Buildings can catch fire by
> wrong boards!!
> 
> Later part difficult for me to read.  (My English not powerful --please 
> excuse.)
> I will make my fullest efforts to read on your recommend 

Hell No! I only asked you to read the first page! 
[And 'Mr. Mark' will scold]

> but I not
> clear the connection with computers, programming, computer science and
> so on.  Also this Mr. Mark Lawrence question.

Once you get that buildings can catch fire by wrong terminology you should get 
that:
- the term 'Turing machine' can make people think its a machine even though its 
a mathematical formalism
- the term 'λ-calculus' (partly due to the word calculus and partly due to the 
greek lambda) makes people think its mathematics even though its a 
computational framework
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Encoding of surrogate code points to UTF-8

[Steven D'Aprano]

I think this is a bug in Python's UTF-8 handling, but I'm not sure.

If I've read the Unicode FAQs correctly, you cannot encode *lone* 
surrogate code points into UTF-8:

http://www.unicode.org/faq/utf_bom.html#utf8-5

Sure enough, using Python 3.3:

py> surr = '\udc80'
py> surr.encode('utf-8')
Traceback (most recent call last):
  File "", line 1, in 
UnicodeEncodeError: 'utf-8' codec can't encode character '\udc80' in 
position 0: surrogates not allowed


But reading the previous entry in the FAQs:

http://www.unicode.org/faq/utf_bom.html#utf8-4

I interpret this as meaning that I should be able to encode valid pairs 
of surrogates. So if I find a code point that encodes to a surrogate pair 
in UTF-16:

py> c = '\N{LINEAR B SYLLABLE B038 E}'
py> surr_pair = c.encode('utf-16be')
py> print(surr_pair)
b'\xd8\x00\xdc\x01'


and then use those same values as the code points, I ought to be able to 
encode to UTF-8, as if it were the same \N{LINEAR B SYLLABLE B038 E} code 
point. But I can't:


py> s = '\ud800\udc01'
py> s.encode('utf-8')
Traceback (most recent call last):
  File "", line 1, in 
UnicodeEncodeError: 'utf-8' codec can't encode character '\ud800' in 
position 0: surrogates not allowed


Have I misunderstood? I think that Python is being too strict about 
rejecting surrogate code points. It should only reject lone surrogates, 
or invalid pairs, not valid pairs. Have I misunderstood the Unicode FAQs, 
or is this a bug in Python's handling of UTF-8?



-- 
Steven
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Re: Multiprocessing and Multithreading

[Grant Edwards]

On 2013-10-08, Mark Lawrence  wrote:
> On 08/10/2013 06:34, Chandru Rajendran wrote:
>> Hi all,
>>
>> Please give me an idea about Multiprocessing and Multithreading.
>>
>> Thanks & Regards,
>>
>> Chandru
>>
>
> I'll assume that you're a newbie so I'll keep it simple. 
> Multiprocessing is about more than one process and multithreading is 
> about more than one thread.

I doubt a newbie knows the difference between a thread and a process.

Threads share all memory and global variabls.  They can communicate
with each other through global variables.

Processes are completely isolated from each other and much communicate
with each other through mechanisms provided by the OS (e.g. sockets,
mailboxes, pipes, files).

-- 
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  at   still in the HAIR DRYER?
  gmail.com
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Re: class implementation

[markotaht]

Parent class is at the link. 

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Re: Image manipulation

[markotaht]

First helpful advice i have gotten from this forum

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Re: Cookie gets changed when hit comes from a referrer

[Νίκος Αλεξόπουλος]

Στις 8/10/2013 2:08 μμ, ο/η Ian Kelly έγραψε:

On Tue, Oct 8, 2013 at 4:04 AM, Νίκος Αλεξόπουλος  wrote:

I use this code to retrive or set a cookie to the visitor's browser if
present and identify him bu it.

All work well except the situation where the user visits my webpage by
clicking a backlink on another wbpage.

Then for some reason the cookieID changes to another value thus a new entry
appears into the database when insert happens.

What cna i do about that?


This question is really about HTTP, not Python, so you'd have better
luck asking elsewhere.  The most likely possibility is that the domain
doesn't match.  For example, the cookie is set for the domain
www.foo.com, and the other webpage is linking to foo.com.  Another
possibility is that the cookie is expiring because the browser session
was terminated, not because of anything to do with the other webpage.
Or it could simply be a bug or unusual setting in whatever browser
you're using to test it.



When i direct hit http://superhost.gr the cookie remains the same it is 
not lost.


Also i have set:
ookie['ID']['expires'] = 60*60*24*365   #this cookie will expire in a 
year

but that didnt also help much because the cookie is also changing when 
the hit comes through a referrer.


So, i cannot se the cookie down to its feet my whole insert or update 
procedure breaks and i have duplicate entried for the same hostnames.


Where shoudl i rely to identify a visitor?
I was relying on tis hostname(although i know that after a router reset) 
it changes, and then couple days ago i was thiking of relying to a 
cookie that i would/set retrive from the vistirs browser, but if it 
changes all the time i cannot evan rely to that.


--
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Re: Formal-ity and the Church-Turing thesis

[Robert Day]

On 08/10/13 14:11, Steven D'Aprano wrote:

On Tue, 08 Oct 2013 18:16:01 +0530, Ravi Sahni wrote:



Presently Sir, I wish to ask single question: What you mean "wave our
hands"??

It is an idiom very common in Australia. (It may not be well known in the
rest of the English-speaking world.) It means to figuratively flap one's
hands around in the air while skipping over technical details or
complications.
It's known elsewhere as well (though mostly in technical circles) - it's 
in the Jargon File as http://www.catb.org/jargon/html/H/handwave.html. 



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converting letters to numbers

[kjakupak]

I have to define a function add(c1, c2), where c1 and c2 are capital letters; 
the return value should be the sum (obtained by converting the letters to 
numbers, adding mod 26, then converting back to a capital letter). 

All I have so far is:

def add(c1, c2):
ord(c1) - ord('a') + 1
ord(c2) - ord('a') + 1

I know I need to use ord and chr, just not sure how.
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Re: Image manipulation

[Steven D'Aprano]

On Tue, 08 Oct 2013 07:15:46 -0700, markotaht wrote:

> First helpful advice i have gotten from this forum

If you insist on dropping cryptic comments with bad spelling, incoherent 
sentences, and a complete lack of any context, it might be the last 
advice you get too.

Please help us to help you. We are not mind readers, we cannot read your 
mind and magically understand what you are talking about. Please include 
content when replying to an posts. Please take the time to try to explain 
your questions, with proper grammar and syntax and spelling. We will make 
allowances if English is not your native language, but we won't make 
allowances if you are just being lazy.

Please show small code snippets that demonstrate the problem. You should 
read this site: even though it is written for Java, the basic ideas hold 
for Python as well.

http://sscce.org


Remember that we are volunteers and we are not being paid to help you. 
The harder you make it for us to understand your posts, the less likely 
we are to solve your problem.


-- 
Steven
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Re: parsing email from stdin

[Andreas Perstinger]

On 08.10.2013 14:20, Antoon Pardon wrote:

As I don't know what encoding these messages will be in, I thought it
would be prudent to read stdin as binary data.

Using python 3.3 on a debian box I have the following code.

#!/usr/bin/python3

import sys
from email import message_from_file

sys.stdin = sys.stdin.detach()
msg = message_from_file(sys.stdin)


Looking at the docs, I've found there is also "message_from_binary_file" 
which works for me with your code.


http://docs.python.org/3/library/email.parser.html#email.message_from_binary_file

Bye, Andreas
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Re: Cookie gets changed when hit comes from a referrer

[Νίκος Αλεξόπουλος]

Στις 8/10/2013 2:08 μμ, ο/η Ian Kelly έγραψε:

This question is really about HTTP, not Python, so you'd have better
luck asking elsewhere.  The most likely possibility is that the domain
doesn't match.  For example, the cookie is set for the domain
www.foo.com, and the other webpage is linking to foo.com.


I think this is the problem but iam not sure entirely how you mean.
Can you please explain it a bit more?

Shall i change 	cookie['ID']['path'] = '/' to something else so that 
never happens?


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Re: converting letters to numbers

[Robert Day]

On 08/10/13 15:28, kjaku...@gmail.com wrote:

I have to define a function add(c1, c2), where c1 and c2 are capital letters; 
the return value should be the sum (obtained by converting the letters to 
numbers, adding mod 26, then converting back to a capital letter).

Can you give some expected outputs? For example, add('A', 'B') should 
presumably return 'C', and add('M', 'B') should presumably return 'O', 
but what about add('A', 'A') or add('Z', 'Z')?


It feels like the only tricky bit is mapping letters to numbers (i.e. 
does A equal 1 or 0?), which you'd do by subtracting a fixed value from 
the result of chr. Once you've done that, you'd do the arithmetic to get 
a number between 1 and 26 (or 0 and 25), then add the same fixed value 
to that and call ord on the result.

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Re: JUST GOT HACKED

[Pat Johnson]

I don't think you are allowed to use the word dumbass to describe anyone or 
anything buddy.



On Tuesday, October 1, 2013 9:42:31 AM UTC-4, Ferrous Cranus wrote:
> Στις 1/10/2013 4:27 μμ, ο/η Chris “Kwpolska” Warrick έγραψε:
> 
> > On Tue, Oct 1, 2013 at 3:15 PM, Νίκος  wrote:
> 
> >> Στις 1/10/2013 4:06 μμ, ο/η Mark Lawrence έγραψε:
> 
> >>>
> 
> >>> On 01/10/2013 10:58, Νίκος wrote:
> 
> 
> 
>  Just logged in via FTP to my server and i saw an uploade file named
> 
>  "Warnign html"
> 
> 
> 
>  Contents were:
> 
> 
> 
>  WARNING
> 
> 
> 
>  I am incompetent. Do not hire me!
> 
> 
> 
>  Question:
> 
> 
> 
>  WHO AND MOST IMPORTNTANLY HOW DID HE MANAGED TO UPLOAD THIS FILE ON MY
> 
>  ACCOUNT?
> 
> 
> 
>  PLEASE ANSWER ME, I WONT GET MAD, BUT THIS IS AN IMPORTANT SECURITY RISK.
> 
> 
> 
>  SOMEONES MUST HAVE ACCESS TO MY ACCOUNT, DOES THE SOURCE CODE OF MY MAIN
> 
>  PYTHON SCRIPT APPEARS SOMEPLACE AGAIN?!?!
> 
> >>>
> 
> >>>
> 
> >>> Would you please stop posting, I've almost burst my stomach laughing at
> 
> >>> this.  You definetely have a ready made career writing comedy.
> 
> >>
> 
> >>
> 
> >> Okey smartass,
> 
> >>
> 
> >> Try to do it again, if you be successfull again i'll even congratulate you
> 
> >> myself.
> 
> >>
> 
> >> --
> 
> >> https://mail.python.org/mailman/listinfo/python-list
> 
> >
> 
> > It looks like you are accusing someone of doing something without any
> 
> > proof whatsoever.  Would you like help with the fallout of the lawsuit
> 
> > that I hope Mark might (should!) come up with?i'am
> 
> >
> 
> > Speaking of “try again”, I doubt it would be hard…  As long as a FTP
> 
> > daemon is running somewhere (and you clearly do not know better); or
> 
> > even you have a SSH daemon and you do not know better, an attacker
> 
> > can:
> 
> >
> 
> > a) wait for you to publish your password yet again;
> 
> > b) get you to download an exploit/keylogger/whatever;
> 
> > c) brute-force.
> 
> >
> 
> > Well, considering it’s unlikely you actually have a long-as-shit
> 
> > password, (c) is the best option.  Unless your password is very long,
> 
> > in which case is not.
> 
> >
> 
> > I’m also wondering what language your password is in.  If you actually
> 
> > used a Greek phrase, how long will it take you to get locked out due
> 
> > to encoding bullshit?
> 
> 
> 
> Like i use grek letter for my passwords or like i'am gonna fall for any 
> 
> of your 3 dumbass reasons.
> 
> 
> 
> I already foudn the weakness and corrected it.

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Re: converting letters to numbers

[kjakupak]

On Tuesday, October 8, 2013 10:47:39 AM UTC-4, Robert Day wrote:
> On 08/10/13 15:28, kjaku...@gmail.com wrote:
> 
> Can you give some expected outputs? For example, add('A', 'B') should 
> 
> presumably return 'C', and add('M', 'B') should presumably return 'O', 
> 
> but what about add('A', 'A') or add('Z', 'Z')?
> 
> 
> 
> It feels like the only tricky bit is mapping letters to numbers (i.e. 
> 
> does A equal 1 or 0?), which you'd do by subtracting a fixed value from 
> 
> the result of chr. Once you've done that, you'd do the arithmetic to get 
> 
> a number between 1 and 26 (or 0 and 25), then add the same fixed value 
> 
> to that and call ord on the result.

Expected output is add('C', 'E') returns 'G'; where 'C' and 'E' correspond to 2 
and 4 respectively with sum 6, corresponding to 'G'.
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Re: JUST GOT HACKED

[Pat Johnson]

>From what I gather he was viewing files uploaded to the ftp folder and found 
>this warning.html file contained within... So my take on it is, someone just 
>uploaded it and this guy is freaking out making a buffoon out of himself.
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Re: Image manipulation

[markotaht]

teisipäev, 8. oktoober 2013 17:26.33 UTC+3 kirjutas Steven D'Aprano:
> On Tue, 08 Oct 2013 07:15:46 -0700, markotaht wrote:
> 
> 
> 
> > First helpful advice i have gotten from this forum
> 
> 
> 
> If you insist on dropping cryptic comments with bad spelling, incoherent 
> 
> sentences, and a complete lack of any context, it might be the last 
> 
> advice you get too.
> 
> 
> 
> Please help us to help you. We are not mind readers, we cannot read your 
> 
> mind and magically understand what you are talking about. Please include 
> 
> content when replying to an posts. Please take the time to try to explain 
> 
> your questions, with proper grammar and syntax and spelling. We will make 
> 
> allowances if English is not your native language, but we won't make 
> 
> allowances if you are just being lazy.
> 
> 
> 
> Please show small code snippets that demonstrate the problem. You should 
> 
> read this site: even though it is written for Java, the basic ideas hold 
> 
> for Python as well.
> 
> 
> 
> http://sscce.org
> 
> 
> 
> 
> 
> Remember that we are volunteers and we are not being paid to help you. 
> 
> The harder you make it for us to understand your posts, the less likely 
> 
> we are to solve your problem.
> 
> 
> 
> 
> 
> -- 
> 
> Steven

Well english isnt my native language, and there are things i just dont know how 
to explain in any language. And i cant give all the codes i am using, since 
there are loads of pieces i do not own, but i know the people who made them.
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Re: Image manipulation

[markotaht]

I rembembered a bit too late, are there any good tutorials for Pillow? 
ImageTk.PhotoImage() keeps giving me error that there isnt such a method.
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Re: converting letters to numbers

[Joel Goldstick]

You wrote this:

def add(c1, c2):
ord(c1) - ord('a') + 1
ord(c2) - ord('a') + 1

First of all, this looks like homework.  People will help you with
concepts here, but most frown on just providing answers.  With that in
mind look at this:

>>> ord('A')
65
>>> ord('a')
97
>>>

In your assignment you refer to Upper case letters.  In your code you
take the ordinal value of lower case 'a'


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Re: Encoding of surrogate code points to UTF-8

[Neil Cerutti]

On 2013-10-08, Steven D'Aprano  wrote:
> py> c = '\N{LINEAR B SYLLABLE B038 E}'
> py> surr_pair = c.encode('utf-16be')
> py> print(surr_pair)
> b'\xd8\x00\xdc\x01'
>
> and then use those same values as the code points, I ought to be able to 
> encode to UTF-8, as if it were the same \N{LINEAR B SYLLABLE B038 E} code 
> point. But I can't:
>
> py> s = '\ud800\udc01'
> py> s.encode('utf-8')
> Traceback (most recent call last):
>   File "", line 1, in 
> UnicodeEncodeError: 'utf-8' codec can't encode character '\ud800' in 
> position 0: surrogates not allowed
>
> Have I misunderstood? I think that Python is being too strict
> about rejecting surrogate code points. It should only reject
> lone surrogates, or invalid pairs, not valid pairs. Have I
> misunderstood the Unicode FAQs, or is this a bug in Python's
> handling of UTF-8?

>From RFC 3629:

  The definition of UTF-8 prohibits encoding character numbers
  between U+D800 and U+DFFF, which are reserved for use with the
  UTF-16 encoding form (as surrogate pairs) and do not directly
  represent characters.  When encoding in UTF-8 from UTF-16 data,
  it is necessary to first decode the UTF-16 data to obtain
  character numbers, which are then encoded in UTF-8 as described
  above.  This contrasts with CESU-8 [CESU-8], which is a
  UTF-8-like encoding that is not meant for use on the Internet.
  CESU-8 operates similarly to UTF-8 but encodes the UTF-16 code
  values (16-bit quantities) instead of the character number
  (code point).  This leads to different results for character
  numbers above 0x; the CESU-8 encoding of those characters
  is NOT valid UTF-8.

The Wikipedia article points out:

  Whether an actual application should [refuse to encode these
  character numbers] is debatable, as it makes it impossible to
  store invalid UTF-16 (that is, UTF-16 with unpaired surrogate
  halves) in a UTF-8 string. This is necessary to store unchecked
  UTF-16 such as Windows filenames as UTF-8. It is also
  incompatible with CESU encoding (described below).

So Python's interpretation is conformant, though not without some
disadvantages.

In any case, "\ud800\udc01" isn't a valid unicode string. In a
perfect world it would automatically get converted to
'\u00010001' without intervention.

-- 
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Re: Encoding of surrogate code points to UTF-8

[Pete Forman]

Steven D'Aprano  writes:

> I think this is a bug in Python's UTF-8 handling, but I'm not sure.
[snip]
> py> s = '\ud800\udc01'
> py> s.encode('utf-8')
> Traceback (most recent call last):
>   File "", line 1, in 
> UnicodeEncodeError: 'utf-8' codec can't encode character '\ud800' in 
> position 0: surrogates not allowed
>
>
> Have I misunderstood? I think that Python is being too strict about 
> rejecting surrogate code points. It should only reject lone surrogates, 
> or invalid pairs, not valid pairs. Have I misunderstood the Unicode FAQs, 
> or is this a bug in Python's handling of UTF-8?

http://www.unicode.org/versions/Unicode6.2.0/ch03.pdf

D75 Surrogate pair: A representation for a single abstract character
  that consists of a sequence of two 16-bit code units, where the first
  value of the pair is a high-surrogate code unit and the second value
  is a low-surrogate code unit.

* Surrogate pairs are used only in UTF-16. (See Section 3.9, Unicode
  EncodingForms.)

* Isolated surrogate code units have no interpretation on their own.
  Certain other isolated code units in other encoding forms also have no
  interpretation on their own. For example, the isolated byte [\x80] has
  no interpretation in UTF-8; it can be used only as part of a multibyte
  sequence. (See Table 3-7). It could be argued that this line by itself
  should raise an error.


That first bullet indicates that it is indeed illegal to use surrogate
pairs in UTF-8 or UTF-32.
-- 
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Re: parsing email from stdin

[Antoon Pardon]

Op 08-10-13 16:24, Andreas Perstinger schreef:

On 08.10.2013 14:20, Antoon Pardon wrote:

As I don't know what encoding these messages will be in, I thought it
would be prudent to read stdin as binary data.

Using python 3.3 on a debian box I have the following code.

#!/usr/bin/python3

import sys
from email import message_from_file

sys.stdin = sys.stdin.detach()
msg = message_from_file(sys.stdin)


Looking at the docs, I've found there is also "message_from_binary_file"
which works for me with your code.

http://docs.python.org/3/library/email.parser.html#email.message_from_binary_file



I can't try that out right now, but I had a look at the code and the
ByteParser that is mentioned their looks like this:

class BytesFeedParser(FeedParser):
"""Like FeedParser, but feed accepts bytes."""

def feed(self, data):
super().feed(data.decode('ascii', 'surrogateescape'))


Somehow I doubt that trying to decode my utf-8 stream as if it was
ascii will work.

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Re: converting letters to numbers

[random832]

On Tue, Oct 8, 2013, at 10:28, kjaku...@gmail.com wrote:
> I have to define a function add(c1, c2), where c1 and c2 are capital
> letters; the return value should be the sum (obtained by converting the
> letters to numbers, adding mod 26, then converting back to a capital
> letter). 
> 
> All I have so far is:
> 
> def add(c1, c2):
> ord(c1) - ord('a') + 1
> ord(c2) - ord('a') + 1
> 
> I know I need to use ord and chr, just not sure how.

Your description says capital letters, but 'a' is a lowercase letter.

Does "mod 26" means A is 1, or is it 0? i.e., is A+A = B or is it A?

What should your function do if the letter isn't a capital letter from
the basic set of 26 English letters?
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Re: Code golf challenge: XKCD 936 passwords

[Denis McMahon]

On Tue, 08 Oct 2013 08:33:48 -0400, Roy Smith wrote:

> In article ,
>  Chris Angelico  wrote:
> 
>> On Tue, Oct 8, 2013 at 5:48 PM,   wrote:
>> > And if we were actually trying then that filename should just be
>> > "/w".
>> > Would get rid of another 19 chars.
>> 
>> I'm working this on the assumption that the dictionary file already
>> exists (that's where it is on my Debian Linux systems, for instance)
>> and shouldn't be moved :)

> In the old days, it used to be /usr/dict/words.  Port Python to v6, and
> save another 6 characters :-)

Doesn't matter where it is, a link to it exists at "/w" now ;)

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Re: converting letters to numbers

[kjakupak]

On Tuesday, October 8, 2013 11:36:51 AM UTC-4, rand...@fastmail.us wrote:
> 
> 
> 
> Your description says capital letters, but 'a' is a lowercase letter.
> 
> 
> 
> Does "mod 26" means A is 1, or is it 0? i.e., is A+A = B or is it A?
> 
> 
> 
> What should your function do if the letter isn't a capital letter from
> 
> the basic set of 26 English letters?

A is 0. 

Transfer it to an uppercase letter if it's a letter, if it's not then an error.
This isn't right, I know, just testing around

def add(c1, c2):
ans = ''
for i in c1 + c2:
ans += chrord(i)-65))%26) + 65)
return ans
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Re: Code golf challenge: XKCD 936 passwords

[random832]

On Tue, Oct 8, 2013, at 2:45, sprucebond...@gmail.com wrote:
> On Monday, October 7, 2013 8:17:21 PM UTC-10, Chris Angelico wrote:
> > print(*__import__("random").sample(open("/usr/share/dict/words").read().split("\n"),4))
> >  # 87
> 
> import random as r
> print(*r.sample(open("/usr/share/dict/words").readlines(),4)) # 80

How about this? My version is also portable to systems with different
file locations, and localizable to different language dictionaries (Some
assembly required).

import sys,random
print(*map(str.strip,random.sample(list(sys.stdin),4))) # 73

Importing random as r doesn't actually save anything, since " as r" is
the same five characters you saved from the one use of it.
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Re: Re for Apache log file format

[Denis McMahon]

On Mon, 07 Oct 2013 23:33:31 -0700, Sam Giraffe wrote:

> I am trying to split up the re pattern for Apache log file format and
> seem to be having some trouble in getting Python to understand
> multi-line pattern:

Aiui apache log format uses space as delimiter, encapsulates strings in 
'"' characters, and uses '-' as an empty field.

So I think every element should match: (\S+|"[^"]+"|-) and there should 
be \s+ between elements.

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Re: Encoding of surrogate code points to UTF-8

[Neil Cerutti]

On 2013-10-08, Neil Cerutti  wrote:
> In any case, "\ud800\udc01" isn't a valid unicode string. In a
> perfect world it would automatically get converted to
> '\u00010001' without intervention.

This last paragraph is erroneous. I must have had a typo in my
testing.

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Re: converting letters to numbers

[random832]

On Tue, Oct 8, 2013, at 11:44, kjaku...@gmail.com wrote:
> def add(c1, c2):
> ans = ''

This only makes sense if your answer is going to be multiple characters.

> for i in c1 + c2:

This line concatenates the strings together.

> ans += chrord(i)-65))%26) + 65)

The way you are doing the modulus, this results in - well, let me
illustrate:

>>> add('','WXYZ[\]^_`abcde')
'WXYZABCDEFGHIJK'
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Re: Re for Apache log file format

[Skip Montanaro]

> Aiui apache log format uses space as delimiter, encapsulates strings in
> '"' characters, and uses '-' as an empty field.

Specifying the field delimiter as a space, you might be able to use
the csv module to read these. I haven't done any Apache log file work
since long before the csv module was available, but it just might
work.

Skip
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Re: Cookie gets changed when hit comes from a referrer

[Denis McMahon]

On Tue, 08 Oct 2013 13:04:34 +0300, Νίκος Αλεξόπουλος wrote:

> I use this code to retrive or set a cookie to the visitor's browser if
> present and identify him bu it.

You are aware that using cookies to track a user who doesn't want to be 
tracked won't work, because he'll just tell his browser to not use 
cookies, aren't you.

Nick, if a user doesn't want to be tracked, you can't track them. The 
user controls all the data their machine sends to you. This means that 
they can manipulate it. Nothing you can do will prevent this.

-- 
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Re: converting letters to numbers

[Mark Lawrence]

On 08/10/2013 15:28, kjaku...@gmail.com wrote:

I have to define a function add(c1, c2), where c1 and c2 are capital letters; 
the return value should be the sum (obtained by converting the letters to 
numbers, adding mod 26, then converting back to a capital letter).



I'd say the requirement is lacking in that no encoding is specified.


All I have so far is:

def add(c1, c2):
 ord(c1) - ord('a') + 1
 ord(c2) - ord('a') + 1

I know I need to use ord and chr, just not sure how.



I'll further observe from your later replies that you're suffering from 
the highly contagious, highly virulent double line spacing disease. 
This is known to cause severe eye strain leading to blindness.  In can 
be cured by purchasing medication here 
https://wiki.python.org/moin/GoogleGroupsPython


--
Roses are red,
Violets are blue,
Most poems rhyme,
But this one doesn't.

Mark Lawrence

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Re: Cookie gets changed when hit comes from a referrer

[Νίκος Αλεξόπουλος]

Στις 8/10/2013 6:55 μμ, ο/η Denis McMahon έγραψε:

On Tue, 08 Oct 2013 13:04:34 +0300, Νίκος Αλεξόπουλος wrote:


I use this code to retrive or set a cookie to the visitor's browser if
present and identify him bu it.


You are aware that using cookies to track a user who doesn't want to be
tracked won't work, because he'll just tell his browser to not use
cookies, aren't you.

Nick, if a user doesn't want to be tracked, you can't track them. The
user controls all the data their machine sends to you. This means that
they can manipulate it. Nothing you can do will prevent this.



Yes iam aware of that, but its the best trcking method i can think of.
Tracking just the hostname is not accurate since with every router 
restart, that info is changing.


Tracking the visitor by settign a cookie to its browser is not 
perfect/accurate since he can manipulate its broswer data or flush the 
cookies but this is the best one can do after having people register on 
the webiste.


Or perhaps trying to identify the cookie + hostname is even better.

Can you help me with this particuler problem please?

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Re: Code golf challenge: XKCD 936 passwords

[Tim Chase]

On 2013-10-08 15:36, Denis McMahon wrote:
> On Tue, 08 Oct 2013 08:33:48 -0400, Roy Smith wrote:
> > In the old days, it used to be /usr/dict/words.  Port Python to
> > v6, and save another 6 characters :-)
> 
> Doesn't matter where it is, a link to it exists at "/w" now ;)

You prodigal...wasting a "/".  I just symlinked it from my current
working directory so it exists at "w". ;-)

-tkc


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Re: Code golf challenge: XKCD 936 passwords

[Tim Chase]

On 2013-10-08 17:17, Chris Angelico wrote:
> Who's up for some fun? Implement an XKCD-936-compliant password
> generator in Python 3, in less code than this:
> 
> print(*__import__("random").sample(open("/usr/share/dict/words").read().split("\n"),4))
> 
> Second challenge: Use it for generating all your passwords :)

UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position
9104: ordinal not in range(128)

-tkc


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Re: class-private names and the Zen of Python

[Ned Batchelder]

On 10/8/13 7:15 AM, Marco Buttu wrote:



Also, as Terry mentions, no one has ever assigned the two names you
show,


Sincerely, I can not now if someone has assigned (or will assegne) in 
such way...


If you explain more about what you are building, and where this crops up 
as a problem, we can help come up with a solution.


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Re: Encoding of surrogate code points to UTF-8

[MRAB]

On 08/10/2013 16:23, Pete Forman wrote:

Steven D'Aprano  writes:


I think this is a bug in Python's UTF-8 handling, but I'm not sure.

[snip]

py> s = '\ud800\udc01'
py> s.encode('utf-8')
Traceback (most recent call last):
  File "", line 1, in 
UnicodeEncodeError: 'utf-8' codec can't encode character '\ud800' in
position 0: surrogates not allowed


Have I misunderstood? I think that Python is being too strict about
rejecting surrogate code points. It should only reject lone surrogates,
or invalid pairs, not valid pairs. Have I misunderstood the Unicode FAQs,
or is this a bug in Python's handling of UTF-8?


http://www.unicode.org/versions/Unicode6.2.0/ch03.pdf

D75 Surrogate pair: A representation for a single abstract character
   that consists of a sequence of two 16-bit code units, where the first
   value of the pair is a high-surrogate code unit and the second value
   is a low-surrogate code unit.

* Surrogate pairs are used only in UTF-16. (See Section 3.9, Unicode
   EncodingForms.)

* Isolated surrogate code units have no interpretation on their own.
   Certain other isolated code units in other encoding forms also have no
   interpretation on their own. For example, the isolated byte [\x80] has
   no interpretation in UTF-8; it can be used only as part of a multibyte
   sequence. (See Table 3-7). It could be argued that this line by itself
   should raise an error.


That first bullet indicates that it is indeed illegal to use surrogate
pairs in UTF-8 or UTF-32.


The only time you should get a surrogate pair in a Unicode string is in
a narrow build, which doesn't exist in Python 3.3 and later.

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Re: parsing email from stdin

[Andreas Perstinger]

On 08.10.2013 17:25, Antoon Pardon wrote:

Op 08-10-13 16:24, Andreas Perstinger schreef:

Looking at the docs, I've found there is also "message_from_binary_file"
which works for me with your code.

http://docs.python.org/3/library/email.parser.html#email.message_from_binary_file



I can't try that out right now, but I had a look at the code and the
ByteParser that is mentioned their looks like this:

class BytesFeedParser(FeedParser):
  """Like FeedParser, but feed accepts bytes."""

  def feed(self, data):
  super().feed(data.decode('ascii', 'surrogateescape'))


Somehow I doubt that trying to decode my utf-8 stream as if it was
ascii will work.


Actually it does work:

$ cat testmail.txt
From: "someone" 
To: "me" 
Subject: something
Content-Type: text/plain; charset="UTF-8";
Content-Transfer-Encoding: 8bit

foo bar AÄÖÜĎӅ baz

$ file testmail.txt
testmail.txt: news or mail, UTF-8 Unicode text

$ cat foo.py
#!/usr/bin/python3

import sys
from email import message_from_binary_file

sys.stdin = sys.stdin.detach()
msg = message_from_binary_file(sys.stdin)

print("from: ", msg['From'])
print("to: ", msg['To'])
print("subject: ", msg['Subject'])
print("body: ", msg.get_payload())

$ ./foo.py < testmail.txt
from:  "someone" 
to:  "me" 
subject:  something
body:  foo bar AÄÖÜĎӅ baz

Bye, Andreas
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Re: Cookie gets changed when hit comes from a referrer

[Νίκος Αλεξόπουλος]

Is there any better way to identif a previous visitor? i tried cookies 
which failed for me for the reason i opened this thread and host like 
follows:


# try to locate the visitor
		cur.execute('''SELECT * FROM visitors WHERE counterID = %s and host = 
%s''', (cID, host) )

data = cur.fetchone()

if not data:
# if first time visitor on this page, create new record
			cur.execute('''INSERT INTO visitors (counterID, host, city, useros, 
browser, ref, lastvisit) VALUES (%s, %s, %s, %s, %s, %s, %s)''',

   (cID, host, city, useros, 
browser, ref, lastvisit) )
else:
# since visitor exists just update his record
			cur.execute('''UPDATE visitors SET city = %s, useros = %s, browser = 
%s, ref = %s, hits = hits + 1, lastvisit = %s''', (city, useros, 
browser, ref, lastvisit) )

===

Please tell me if you can think fo something else.

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Re: Code golf challenge: XKCD 936 passwords

[Tobiah]

On 10/08/2013 09:07 AM, Tim Chase wrote:

On 2013-10-08 15:36, Denis McMahon wrote:

On Tue, 08 Oct 2013 08:33:48 -0400, Roy Smith wrote:

In the old days, it used to be /usr/dict/words.  Port Python to
v6, and save another 6 characters :-)


Doesn't matter where it is, a link to it exists at "/w" now ;)


You prodigal...wasting a "/".  I just symlinked it from my current
working directory so it exists at "w". ;-)

-tkc




Yeah, but that's a lot of pixels!  Link it to "'" in the current directory.
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Re: Formal-ity and the Church-Turing thesis

[Mark Janssen]

>> I don't have an infinite stack to implement
>> lambda calculus, but...
>
> And then
>
>> But this is not a useful formalism.  Any particular Program implements
>> a DFA, even as it runs on a TM.  The issue of whether than TM is
>> finite or not can be dismissed because a simple calculation can
>> usually suffice, or at least establish a range "usefulness" so as not
>> to "run out of memory".
>
> Having it both ways aren't you?

I'm just speaking from programmer experience and the fact that most
machines are VonNeumann architecture.  Being that as it is, maxing out
the stack simply happens, and I don't dare do any non-simple
recursion, but otherwise, practically speaking, I can calculate my
memory usage that may grow on the heap so that is effectively a
non-issue.  This may not be an important distinction for computing,
the "art" (Hello ultimate lambda friends), but it is significant for
the computing, the science.

MarkJ
Tacoma, Washington
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Re: Cookie gets changed when hit comes from a referrer

[Joel Goldstick]

On Tue, Oct 8, 2013 at 1:30 PM, Νίκος Αλεξόπουλος  wrote:
> Is there any better way to identif a previous visitor? i tried cookies which
> failed for me for the reason i opened this thread and host like follows:
>
> # try to locate the visitor
> cur.execute('''SELECT * FROM visitors WHERE counterID = %s
> and host = %s''', (cID, host) )
> data = cur.fetchone()
>
> if not data:
> # if first time visitor on this page, create new
> record
> cur.execute('''INSERT INTO visitors (counterID,
> host, city, useros, browser, ref, lastvisit) VALUES (%s, %s, %s, %s, %s, %s,
> %s)''',
>(cID, host, city, useros,
> browser, ref, lastvisit) )
> else:
> # since visitor exists just update his record
> cur.execute('''UPDATE visitors SET city = %s, useros
> = %s, browser = %s, ref = %s, hits = hits + 1, lastvisit = %s''', (city,
> useros, browser, ref, lastvisit) )
> ===
>
> Please tell me if you can think fo something else.

Yes! there is a very simple and comprehensive way to learn about your
visitors.  Use Google Analytics.  Its free, you only need a google
account to open an analytics account.  They give you a small bit of
javascript that you copy and past to your pages.  If you are using a
template to create your pages, this is easy, since you just add google
code to the template.
>
> --
> https://mail.python.org/mailman/listinfo/python-list



-- 
Joel Goldstick
http://joelgoldstick.com
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Re: Code golf challenge: XKCD 936 passwords

[Tobiah]

On 10/07/2013 11:17 PM, Chris Angelico wrote:

Who's up for some fun? Implement an XKCD-936-compliant password
generator in Python 3, in less code than this:

print(*__import__("random").sample(open("/usr/share/dict/words").read().split("\n"),4))

Second challenge: Use it for generating all your passwords :)

[1] https://en.wikipedia.org/wiki/Code_golf
[2] http://xkcd.com/936/

ChrisA



So how about finding the last word that starts with
each lower case letter of the alphabet in turn:

azures
bywords
czars
...

Tobiah
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Re: Encoding of surrogate code points to UTF-8

[wxjmfauth]

>>> sys.version
'3.3.2 (v3.3.2:d047928ae3f6, May 16 2013, 00:03:43) [MSC v.1600 32 bit (Intel)]'
>>> '\ud800'.encode('utf-8')
Traceback (most recent call last):
  File "", line 1, in 
UnicodeEncodeError: 'utf-8' codec can't encode character '\ud800' in position 
0: 
surrogates not allowed
>>> '\ud800'.encode('utf-32-be')
b'\x00\x00\xd8\x00'
>>> '\ud800'.encode('utf-32-le')
b'\x00\xd8\x00\x00'
>>> '\ud800'.encode('utf-32')
b'\xff\xfe\x00\x00\x00\xd8\x00\x00'


jmf
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Re: Cookie gets changed when hit comes from a referrer

[Joel Goldstick]

On Tue, Oct 8, 2013 at 12:04 PM, Νίκος Αλεξόπουλος
 wrote:
> Στις 8/10/2013 6:55 μμ, ο/η Denis McMahon έγραψε:
>
>> On Tue, 08 Oct 2013 13:04:34 +0300, Νίκος Αλεξόπουλος wrote:
>>
>>> I use this code to retrive or set a cookie to the visitor's browser if
>>> present and identify him bu it.
>>
>>
Browser cookies have been defined and around for a very long time.  If
you google "browser cookie tutorial" you can learn how they work --
probably within an hour!.  This will help you find your solution
The first poster pointed out that www.example.com and example.com can
be considered different domains.  You can make a cookie work for both
but you need to understand cookies to learn how.

This is off topic, ... again!

> https://mail.python.org/mailman/listinfo/python-list



-- 
Joel Goldstick
http://joelgoldstick.com
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Re: Cookie gets changed when hit comes from a referrer

[Denis McMahon]

On Tue, 08 Oct 2013 19:04:37 +0300, Νίκος Αλεξόπουλος wrote:

> Can you help me with this particuler problem please?

Unfortunately I can't, because I am unable to reproduce the problem you 
describe.

When I load my test page in the browser, then replace it with something 
else by entering an address in the address bar and pressing return, then 
use the back link followed by the reload one, I am back at my test page 
with the original cookie value.

Of course, this is using my cookie etc code and mechanisms, and not 
yours 

Now, either it's an issue in your python implementation of cookie 
handling which isn't happening in my implementation, or it's something to 
do with the way that your system passes data around (cgi) that doesn't 
happen in mine (mod_wsgi), or it's happening in the browser you're 
testing in, but not in my browser.

Have you checked the cookie jar in the browser to see what value the 
cookie has? Is that the value you think it should have? Note that 
checking the cookie jar is a browser topic, not a python topic, so if you 
don't know how to do that you're going to have to find the right place to 
ask, WHICH IS NOT HERE!

Ideally you need to check what the server thinks it's setting the cooking 
to, what the browser thinks it received as the cookie, and what the 
server gets back afterwards to work out where the error is happening.

-- 
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Re: Code golf challenge: XKCD 936 passwords

[sprucebondera]

On Tuesday, October 8, 2013 5:47:56 AM UTC-10, rand...@fastmail.us wrote:
> Importing random as r doesn't actually save anything, since " as r" is
> the same five characters you saved from the one use of it.

I realize, it just looks nicer than the original __import__, and since it 
doesn't add any characters... 
The optimization was using readlines.
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Re: Code golf challenge: XKCD 936 passwords

[Chris Angelico]

On Wed, Oct 9, 2013 at 7:27 AM,   wrote:
> On Tuesday, October 8, 2013 5:47:56 AM UTC-10, rand...@fastmail.us wrote:
>> Importing random as r doesn't actually save anything, since " as r" is
>> the same five characters you saved from the one use of it.
>
> I realize, it just looks nicer than the original __import__, and since it 
> doesn't add any characters...
> The optimization was using readlines.

Are you aware that readlines keeps the \n at the end of each line,
though? Looks a lot less clean in its output that way. That's why I
used .split() in the first place.

ChrisA
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How to help us to help you (was: Image manipulation)

[Ben Finney]

markot...@gmail.com writes:

> Well english isnt my native language, and there are things i just dont
> know how to explain in any language.

I sympathise with attempting to explain things in a foreign language.
Sorry that you have that difficulty here.

But the rest of Steven's advice is sound: you need to help us to help
you.

One way to do that: Please don't use Google Groups to post here, it
mangles your replies in ways that make it difficult for you to be
understood https://wiki.python.org/moin/GoogleGroupsPython>.

> And i cant give all the codes i am using, since there are loads of
> pieces i do not own, but i know the people who made them.

So you need to present examples that are short, self-contained, correct,
compilable http://sscce.org/>. That may entail you writing the
examples for the purpose of posting them here; but do run them yourself
before posting!

You'll often learn about the problem without needing our input if you do
it that way. And if you don't, then you have a tool that will definitely
get you better responses here.

-- 
 \“The problem with television is that the people must sit and |
  `\keep their eyes glued on a screen: the average American family |
_o__) hasn't time for it.” —_The New York Times_, 1939 |
Ben Finney

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Re: converting letters to numbers

[Dave Angel]

On 8/10/2013 10:28, kjaku...@gmail.com wrote:

> I have to define a function add(c1, c2), where c1 and c2 are capital letters; 
> the return value should be the sum (obtained by converting the letters to 
> numbers, adding mod 26, then converting back to a capital letter). 
>
> All I have so far is:
>
> def add(c1, c2):
> ord(c1) - ord('a') + 1
> ord(c2) - ord('a') + 1
>
> I know I need to use ord and chr, just not sure how.


Factor the problem into three functions.  one function converts a
one-character string into an int, or gives an exception if the
character. isn't uppercase ASCII.

Second function converts a small int into a string containing one
uppercase ASCII letter, throwing an exception if negative or above 25.

Third function takes two string arguents, throws an exception if either
of them is not exactly one character in length.  Then it calls the first
function twice, adds the results, modulos it, and calls the second
function, returning its return value.

Which of these is giving you trouble?  Notice you can use the first two
functions to test each other.

-- 
DaveA


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Re: Formal-ity and the Church-Turing thesis

[Chris Angelico]

On Wed, Oct 9, 2013 at 12:11 AM, Steven D'Aprano
 wrote:
> On Tue, 08 Oct 2013 18:16:01 +0530, Ravi Sahni wrote:
>
>>> So in that sense, computers are Turing Machines. Anything a physical
>>> computing device can compute, a Turing Machine could too. The converse
>>> is not true though: a Turing Machine with infinite tape can compute
>>> things where a real physical device would run out of memory, although
>>> it might take longer than anyone is willing to wait.
>>
>> Thanks Sir the detailed explanation. You are offering me many thoughts
>> inside few words so I will need some time to meditate upon the same.
>>
>> Presently Sir, I wish to ask single question: What you mean "wave our
>> hands"??
>
> It is an idiom very common in Australia. (It may not be well known in the
> rest of the English-speaking world.) It means to figuratively flap one's
> hands around in the air while skipping over technical details or
> complications. For example, we often talk about "hand-wavy estimates" for
> how long a job will take: "my hand-wavy estimate is it will take two
> days" is little better than a guess.

A derivative of the term has gone mainstream, too:

http://tvtropes.org/pmwiki/pmwiki.php/Main/HandWave

The term is commonly used when moving to a higher level of abstraction
- we all know a computer doesn't have a soul, can't "feel", and is
ultimately just executing code and crunching numbers, but we handwave
that (eg) the computer "thought" that this program was a risk, and
that's why it quarantined it. When you're trying to explain to some
user that he can't email .EXE files around, it's easier to take the
slightly-inaccurate but simple explanation, hence the handwaves.

ChrisA
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Re: Encoding of surrogate code points to UTF-8

[Terry Reedy]

On 10/8/2013 9:52 AM, Steven D'Aprano wrote:

I think this is a bug in Python's UTF-8 handling, but I'm not sure.

If I've read the Unicode FAQs correctly, you cannot encode *lone*
surrogate code points into UTF-8:

http://www.unicode.org/faq/utf_bom.html#utf8-5

Sure enough, using Python 3.3:

py> surr = '\udc80'


I am pretty sure that if Python were being strict, that would raise an 
error, as the result is not a valid unicode string. Allowing the above 
or not was debated and laxness was allowed for at least the following 
practical reasons.


1. Python itself uses the invalid surrogate codepoints for 
surrogateescape error-handling.

http://www.python.org/dev/peps/pep-0383/

2. Invalid strings are needed for tests ;-)
-- like the one you do next.

3. Invalid strings may be needed for interfacing with other C APIs.


py> surr.encode('utf-8')
Traceback (most recent call last):
   File "", line 1, in 
UnicodeEncodeError: 'utf-8' codec can't encode character '\udc80' in
position 0: surrogates not allowed


Default strict encoding (utf-8 or otherwise) will only encode valid 
unicode strings. Encode invalid strings with surrogate codepoints with 
surrogateescape error handling.



But reading the previous entry in the FAQs:

http://www.unicode.org/faq/utf_bom.html#utf8-4

I interpret this as meaning that I should be able to encode valid pairs
of surrogates.


It says you should be able to 'convert' them, and that the result for 
utf-8 encoding must be a single 4-bytes code for the corresponding 
supplementary codepoint.



So if I find a code point that encodes to a surrogate pair
in UTF-16:

py> c = '\N{LINEAR B SYLLABLE B038 E}'
py> surr_pair = c.encode('utf-16be')
py> print(surr_pair)
b'\xd8\x00\xdc\x01'

and then use those same values as the code points, I ought to be able to
encode to UTF-8, as if it were the same \N{LINEAR B SYLLABLE B038 E} code
point. But I can't:

py> s = '\ud800\udc01'


This is now a string with two invalid codepoints instead of one ;-).
As above, it would be rejected if Python were being strict.


py> s.encode('utf-8')
Traceback (most recent call last):
   File "", line 1, in 
UnicodeEncodeError: 'utf-8' codec can't encode character '\ud800' in
position 0: surrogates not allowed


Have I misunderstood? I think that Python is being too strict about
rejecting surrogate code points.


No, it is being too lax about allowing them at all.

I believe there is an issue on the tracker (maybe closed) about the doc 
for unicode escapes in string literals. Perhaps is should say more 
clearly that inserting surrogates is allowed but results in an invalid 
string that cannot be normally encoded.


--
Terry Jan Reedy

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Re: Encoding of surrogate code points to UTF-8

[Terry Reedy]

On 10/8/2013 5:47 PM, Terry Reedy wrote:

On 10/8/2013 9:52 AM, Steven D'Aprano wrote:



But reading the previous entry in the FAQs:

http://www.unicode.org/faq/utf_bom.html#utf8-4

I interpret this as meaning that I should be able to encode valid pairs
of surrogates.


It says you should be able to 'convert' them, and that the result for
utf-8 encoding must be a single 4-bytes code for the corresponding
supplementary codepoint.


To expand on this: The FAQ question is "How do I convert a UTF-16 
surrogate pair such as  to UTF-8?" utf-16 and utf-8 are both 
byte (or double byte) encodings of codepoints. Direct conversion would 
be 'transcoding', not encoding. Python has a few bytes transcoders and 
one string transcoder (rot_13), listed at the end of

http://docs.python.org/3/library/codecs.html#python-specific-encodings
But in general, one must decode bytes to string and encode back to bytes.


So if I find a code point that encodes to a surrogate pair
in UTF-16:

py> c = '\N{LINEAR B SYLLABLE B038 E}'
py> surr_pair = c.encode('utf-16be')
py> print(surr_pair)
b'\xd8\x00\xdc\x01'

and then use those same values as the code points, I ought to be able to
encode to UTF-8, as if it were the same \N{LINEAR B SYLLABLE B038 E} code
point.


I believe the utf encodings are defined as 1 to 1. If the above worked, 
utf-8 would not be.


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Terry Jan Reedy

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Re: Encoding of surrogate code points to UTF-8

[Steven D'Aprano]

On Tue, 08 Oct 2013 18:00:58 +0100, MRAB wrote:

> The only time you should get a surrogate pair in a Unicode string is in
> a narrow build, which doesn't exist in Python 3.3 and later.

Incorrect.

py> sys.version
'3.3.0rc3 (default, Sep 27 2012, 18:44:58) \n[GCC 4.1.2 20080704 (Red Hat 
4.1.2-52)]'
py> s = '\ud800\udc01'
py> print(len(s))
2
py> import unicodedata as ud
py> for c in s:
... print(ud.category(c))
...
Cs
Cs

s is a string containing two code points making up a surrogate pair.


It is very frustrating that the Unicode FAQs don't always clearly 
distinguish between when they are talking about bytes and when they are 
talking about code points. This area about surrogates is one of places 
where they conflate the two.



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Steven
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Re: Code golf challenge: XKCD 936 passwords

[Rob Day]

On 08/10/13 07:17, Chris Angelico wrote:

Who's up for some fun? Implement an XKCD-936-compliant password
generator in Python 3, in less code than this:

print(*__import__("random").sample(open("/usr/share/dict/words").read().split("\n"),4))



print("imploring epsilon decamp graveyard's")
# Chosen by fair random sampling, guaranteed to be random

Comments don't count as code, right? ;)
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Re: Encoding of surrogate code points to UTF-8

[Steven D'Aprano]

On Tue, 08 Oct 2013 15:14:33 +, Neil Cerutti wrote:

> In any case, "\ud800\udc01" isn't a valid unicode string. 

I don't think this is correct. Can you show me where the standard says 
that Unicode strings[1] may not contain surrogates? I think that is a 
critical point, and the FAQ conflates *encoded strings* (i.e. bytes using 
one of the UTCs) with *Unicode strings*.

The string you give above is is a Unicode string containing two code 
points, the surrogates U+D800 U+DC01, which as far as I am concerned is a 
legal string (subject to somebody pointing me to a definitive source that 
proves it is not). However, it *may or may not* be encodable to bytes 
using UTF-8, -16 or -32.

Just as there are byte sequences that cannot be generated by the UTFs, 
possibly there are code point sequences that cannot be converted to bytes 
using the UTFs.


> In a perfect
> world it would automatically get converted to '\u00010001' without
> intervention.

I certainly hope not, because Unicode string != UTF-16. This is 
equivalent to saying:

When encoding the sequence of code points '\ud800\udc01' to UTF-8 bytes, 
you should get the same result as if you treated the sequence of code 
points as if it were bytes, decoded it using UTF-16, and then encoded 
using UTF-8.

That would be a horrible, horrible design, since it privileges UTF-16 in 
a completely inappropriate way. I *really* hope I am wrong, but I fear 
that is my interpretation of the FAQ.



[1] Sequences of Unicode code points.


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Re: Re for Apache log file format

[Cameron Simpson]

On 08Oct2013 10:59, Skip Montanaro  wrote:
| > Aiui apache log format uses space as delimiter, encapsulates strings in
| > '"' characters, and uses '-' as an empty field.
| 
| Specifying the field delimiter as a space, you might be able to use
| the csv module to read these. I haven't done any Apache log file work
| since long before the csv module was available, but it just might
| work.

You can definitely do this. I pull things out of apache log files
using awk in exactly this fashion. It does rely on each of the
"real" fields having a fixed number of "words" in it. You just stick
the fields back together again.

And also in Python.

I've got a merge-apache-logs script to read multiple logs, presumed
in time order, and produce a single output stream for passing to
log analysis tools:

  https://bitbucket.org/cameron_simpson/css/src/tip/bin/merge-apache-logs

It is a bit of a hack, but useful.

It has an "aptime" function to pull and parse the time field from
the line which starts like this:

def aptime(logline, zones, defaultZone):
  ''' Compute a datetime object from the supplied Apache log line.
  `defaultZone` is the timezone to use if it cannot be deduced.
  '''
  fields = logline.split()
  if len(fields) < 5:
##warning("bad log line: %s", logline)
return None

  dt = None
  tzinfo = None

  # try for desired "[DD/Mon/:HH:MM:SS +hhmm]" format
  humantime, tzinfo = fields[3], fields[4]
  if len(humantime) == 21 \
  and humantime.startswith('[') \
  and tzinfo.endswith(']'):
try:
  dt = datetime.strptime(humantime, "[%d/%b/%Y:%H:%M:%S")
except ValueError, e:
  dt = None
if dt is None:
  tzinfo = None
else:
  tzinfo = tzinfo[:-1]

and proceeeds otherwise (we have a few different log formats in play, alas).

So regexpas are not your only choice here, and possibly not even the best 
choice.

Cheers,
-- 
Cameron Simpson 

This is not a bug. It's just the way it works, and makes perfect sense.
- Tom Christiansen 
I like that line. I hope my boss falls for it.
- Chaim Frenkel 
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Re: Cookie gets changed when hit comes from a referrer

[Νίκος Αλεξόπουλος]

Στις 8/10/2013 10:29 μμ, ο/η Denis McMahon έγραψε:

On Tue, 08 Oct 2013 19:04:37 +0300, Νίκος Αλεξόπουλος wrote:


Can you help me with this particuler problem please?


Unfortunately I can't, because I am unable to reproduce the problem you
describe.

When I load my test page in the browser, then replace it with something
else by entering an address in the address bar and pressing return, then
use the back link followed by the reload one, I am back at my test page
with the original cookie value.

Of course, this is using my cookie etc code and mechanisms, and not
yours 

Now, either it's an issue in your python implementation of cookie
handling which isn't happening in my implementation, or it's something to
do with the way that your system passes data around (cgi) that doesn't
happen in mine (mod_wsgi), or it's happening in the browser you're
testing in, but not in my browser.

Have you checked the cookie jar in the browser to see what value the
cookie has? Is that the value you think it should have? Note that
checking the cookie jar is a browser topic, not a python topic, so if you
don't know how to do that you're going to have to find the right place to
ask, WHICH IS NOT HERE!

Ideally you need to check what the server thinks it's setting the cooking
to, what the browser thinks it received as the cookie, and what the
server gets back afterwards to work out where the error is happening.


Is there something i can try to isolate the problem and make it work?
By whole counters project is based on cookie handling now


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Re: class-private names and the Zen of Python

[Oscar Benjamin]

On Oct 8, 2013 2:26 PM, "Steven D'Aprano" <
steve+comp.lang.pyt...@pearwood.info> wrote:
>
> On Tue, 08 Oct 2013 12:13:48 +0200, Marco Buttu wrote:
>
> > Another question is: where is the place in which this transformation
> > occurs? Is it at the parser level, before the dictionary attribute is
> > gave as argument to the metaclass?
>
> Good question!
>
> I don't have a full answer, but I have a part answer: it occurs before
> the metaclass sees the namespace:
>

I thought it was at the parser level and applied to assignments at class
level and attribute assignments anywhere within a class body.

I'm pretty sure there's no way to control the behaviour from Python code if
that's what the metaclass question is getting at.

Oscar
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Re: class implementation

[Rhodri James]

On Tue, 08 Oct 2013 15:05:26 +0100,  wrote:


Parent class is at the link.


Please quote some context when you reply.  What link?

Then again, I'm not about to click on some random link someone posts to a  
newsgroup.  Apart from being one of the classic ways to get a virus onto  
my computer, it's rather selfish of you.  While your newsgroup posting  
will stay around essentially forever, the link will eventually rot.  At  
some point in the future, no one will be able to follow that link, so no  
one will be able to learn from what you have done.


Please show your working, it makes it so much easier for the rest of us to  
understand what you meant when you use terms so loosely!


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