Re: mutable ints: I think I have painted myself into a corner
Cameron Simpson wrote:
> TL;DR: I think I want to modify an int value "in place".
>
> Yesterday I was thinking about various "flag set" objects I have
> floating around which are essentially bare "object"s whose attributes
> I access, for example:
>
> flags = object()
> flags.this = True
> flags.that = False
>
> and then elsewhere:
>
> if flags.that:
> do that ...
>
> Nice and readable, but I thought to myself: so bulky!
Plus, it doesn't work:
>>> object().this = True
Traceback (most recent call last):
File "", line 1, in
AttributeError: 'object' object has no attribute 'this'
> The use case for flags is essentially boolean/binary, and so a int
> accessed as a bitmask should be smaller.
>
> So I pulled out my BitMask int subclass (which mostly transcribes
> the int as "A|B|C" for readability purposes, partly to dillute Nick
> Coglan's liking for bulky strings over compact ints on readability
> grounds:-), and gave the subclass attribute access.
>
> This works just fine for querying the flags object, with code exactly
> like the "if" statement above.
>
> But setting up a flags object? What I _want_ to write is code like this:
>
> Flags = BitMask('this', 'that')
>
> # set default state
> flags = Flags()
> flags.this = False
> flags.that = True
> ... iterate over some options ...: flags.this = True
>
> and there's my problem. This would modify the int in place. There's
> no way to do that. For the base type (int) this makes perfect sense,
> as they're immutable.
>
> Before I toss this approach and retreat to my former "object"
> technique, does anyone see a way forward to modify an int subclass
> instance in place? (That doesn't break math, preferably; I don't
> do arithmetic with these things but they are, after all, ints...)
No, but you could make
flags = Flags(this=False, that=True)
work.
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Re: How to write fast into a file in python?
On Sun, May 19, 2013 at 3:31 PM, Carlos Nepomuceno wrote: > Thanks Dan! I've never used CPython or PyPy. Will try them later. CPython is the "classic" interpreter, written in C. It's the one you'll get from the obvious download links on python.org. ChrisA -- http://mail.python.org/mailman/listinfo/python-list
RE: How to write fast into a file in python?
ooops! I meant to say Cython. nevermind... > Date: Sun, 19 May 2013 19:21:54 +1000 > Subject: Re: How to write fast into a file in python? > From: ros...@gmail.com > To: python-list@python.org > > On Sun, May 19, 2013 at 3:31 PM, Carlos Nepomuceno > wrote: >> Thanks Dan! I've never used CPython or PyPy. Will try them later. > > CPython is the "classic" interpreter, written in C. It's the one > you'll get from the obvious download links on python.org. > > ChrisA > -- > http://mail.python.org/mailman/listinfo/python-list > -- http://mail.python.org/mailman/listinfo/python-list
Harmonic distortion of a input signal
Hi, I have a task to calculate total distortion of a harmonics, of a signal that i imported from oscilloscope as numpy array. I had no problem drawing its spectrum, and time domain graph, but cant seem to find any functions that calculate TDH. Any help? Best regards -- http://mail.python.org/mailman/listinfo/python-list
Re: Future standard GUI library
On 5/18/13 11:01 PM, llanitedave wrote: I'm curious about how commonly tkinter is actually used among Python app developers as compared to wx, Pyside, or PyQT. I get the impression that more distributed apps are built with wxPython, at least, than tkinter. My impression is far from actual knowledge, of course. I have two commercial apps developed with Tkinter: http://www.codebykevin.com/phynchronicity.html http://www.codebykevin.com/quickwho.html --Kevin -- Kevin Walzer Code by Kevin/Mobile Code by Kevin http://www.codebykevin.com http://www.wtmobilesoftware.com -- http://mail.python.org/mailman/listinfo/python-list
Re: What was the project that made you feel skilled in Python?
In article , Ned Batchelder wrote: > So here's a question for people who remember coming up from beginner: as > you moved from exercises like those in Learn Python the Hard Way, up to > your own self-guided work on small projects, what project were you > working on that made you feel independent and skilled? What program > first felt like your own work rather than an exercise the teacher had > assigned? IIRC, my first production python projects were a bunch of file parsers. We had a bunch of text file formats that we worked with often. I wrote some state-machine based parsers which slurped them up and gave back the contents in some useful data structure. Many of the files were big, so I added an option to write out a pickled version of the data. The parsing code could then check to see if there was a pickle file that was newer than the text version and read that instead. Big win for speed. Then, of course, a bunch of utilities which used this data to do useful things. I remember one of the utilities that turned out to be really popular was a smart data file differ. You feed it two files and it would tell you how they differed (in a way that was more useful than a plain text-based diff). -- http://mail.python.org/mailman/listinfo/python-list
Re: Harmonic distortion of a input signal
On Sun, May 19, 2013 at 8:52 PM, Anti Log wrote: > total distortion of a harmonics I selected this part of your post, right-clicked, and Chrome offered to do a Google search for those words. And, surprise surprise, the first hit is a page that appears to have the mathematics behind it. Now, I don't know how much you trust Google and Wikipedia, but I'm sure you can confirm the maths in some other way. My guess is that there's no function in numpy to do what you're asking... but it shouldn't be too hard to render the formula/e given into Python code. Python's pretty expressive when it comes to algebra. :) ChrisA -- http://mail.python.org/mailman/listinfo/python-list
Re: How to write fast into a file in python?
On 19/05/2013 04:53, Carlos Nepomuceno wrote: Date: Sat, 18 May 2013 22:41:32 -0400 From: da...@davea.name To: python-list@python.org Subject: Re: How to write fast into a file in python? On 05/18/2013 01:00 PM, Carlos Nepomuceno wrote: Python really writes '\n\r' on Windows. Just check the files. That's backwards. '\r\n' on Windows, IF you omit the b in the mode when creating the file. Indeed! My mistake just made me find out that Acorn used that inversion on Acorn MOS. According to this[1] (at page 449) the OSNEWL routine outputs '\n\r'. What the hell those guys were thinking??? :p Doing it that way saved a few bytes. Code was something like this: FFE3.OSASCI CMP #&0D FFE5BNE OSWRCH FFE7.OSNEWL LDA #&0A FFE9JSR OSWRCH FFECLDA #&0D FFEE.OSWRCH ... This means that the contents of the accumulator would always be preserved by a call to OSASCI. "OSNEWL This call issues an LF CR (line feed, carriage return) to the currently selected output stream. The routine is entered at &FFE7." [1] http://regregex.bbcmicro.net/BPlusUserGuide-1.07.pdf -- http://mail.python.org/mailman/listinfo/python-list
Python for philosophers
On May 17, 1:06 am, Citizen Kant wrote: > rusi said: > > > And let me suggest that you follow your own advise -- Can you say what > > you have to say in 1/10th the number of words? Ok if not 1/10th then > > 1/5th? 1-third? > > Thanks for the suggestion. I apologize for being that expansive; maybe you > are right about this. In my world less use to be less. I'll try to review > my doubts in order to express them in a much more concise format. > > Of course this is not trolling at all, and I'm intrigued by how fast > someone can fall into that kind of conclusions... > > I'm pretty much interested in the topic, so I'll review the stuff. You are doing well -- Glad to see that. Except for the subject line. What's with the Fwd-loop? Anyway I have attempted to correct it -- http://mail.python.org/mailman/listinfo/python-list
Re: any cherypy powred sites I can check out?
On Fri, 17 May 2013 11:48:19 +1000, Chris Angelico wrote: > (Caveat: I am not a Catholic, so I haven't much of a clue as to how > confession usually goes.) Forgive OP Father, for he has sinned... -- http://mail.python.org/mailman/listinfo/python-list
Re: Please help with Threading
On Mon, May 20, 2013 at 7:46 AM, Dennis Lee Bieber wrote: > On Sun, 19 May 2013 10:38:14 +1000, Chris Angelico > declaimed the following in gmane.comp.python.general: >> With interpreted code eg in CPython, it's easy to implement preemption >> in the interpreter. I don't know how it's actually done, but one easy >> implementation would be "every N bytecode instructions, context >> switch". It's still done at a lower level than user code (N bytecode > > Which IS how the common Python interpreter does it -- barring the > thread making some system call that triggers a preemption ahead of time > (even time.sleep(0.0) triggers scheduling). Forget if the default is 20 > or 100 byte-code instructions -- as I recall, it DID change a few > versions back. Incidentally, is the context-switch check the same as the check for interrupt signal raising KeyboardInterrupt? ISTR that was another "every N instructions" check. ChrisA -- http://mail.python.org/mailman/listinfo/python-list
Re: Harmonic distortion of a input signal
How can i at least find a peek in FFT spectrum of a square wave ? >From there i could easily build formula. Sorry for bothering but i am new to >Python. -- http://mail.python.org/mailman/listinfo/python-list
Re: Harmonic distortion of a input signal
On 19 May 2013 23:25, wrote: > How can i at least find a peek in FFT spectrum of a square wave ? > From there i could easily build formula. Sorry for bothering but i am new to > Python. Are you the same person who posted the original question? You probably want to use numpy for this. I'm not sure if I understand your question but here goes: First import numpy (you may need to install this first): >>> import numpy as np Create a square wave signal: >>> x = np.zeros(50) >>> x[:25] = -1 >>> x[25:] = +1 >>> x array([-1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1.]) Compute the magnitude spectrum: >>> spect = abs(np.fft.fft(x)[:25]) >>> spect array([ 0., 31.85194222, 0., 10.67342282, 0., 6.47213595, 0., 4.69726931, 0., 3.73254943, 0., 3.13762901, 0., 2.7436023 , 0., 2.47213595, 0., 2.28230601, 0., 2.15105461, 0., 2.06487174, 0., 2.01589594, 0.]) Find the index of the maximum element: >>> np.argmax(spect) 1 So the peak is the lowest non-zero frequency component of the DFT. In Hz this corresponds to a frequency of 1/T where T is the duration of the signal. Oscar -- http://mail.python.org/mailman/listinfo/python-list
Re: Harmonic distortion of a input signal
Yes, sorry logged from another account. Would that work on a numpy array ? Because this signal was imported from oscilloscope as a numpy array. Best regards, -- http://mail.python.org/mailman/listinfo/python-list
Re: Harmonic distortion of a input signal
Got it working, thanks alot :) -- http://mail.python.org/mailman/listinfo/python-list
Re: Harmonic distortion of a input signal
On 5/19/2013 6:49 PM, Oscar Benjamin wrote: import numpy as np Create a square wave signal: x = np.zeros(50) x[:25] = -1 x[25:] = +1 x array([-1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1., 1.]) Compute the magnitude spectrum: spect = abs(np.fft.fft(x)[:25]) spect array([ 0., 31.85194222, 0., 10.67342282, 0., 6.47213595, 0., 4.69726931, 0., 3.73254943, 0., 3.13762901, 0., 2.7436023 , 0., 2.47213595, 0., 2.28230601, 0., 2.15105461, 0., 2.06487174, 0., 2.01589594, 0.]) Find the index of the maximum element: np.argmax(spect) 1 So the peak is the lowest non-zero frequency component of the DFT. In Hz this corresponds to a frequency of 1/T where T is the duration of the signal. While you were answering a specific question, I think the above is a nice tutorial example, because it is more meaningful than arbitrary operations applied to random data. -- http://mail.python.org/mailman/listinfo/python-list
Re: Harmonic distortion of a input signal
One more question. Function np.argmax returns max of non-complex numbers ? Because FFT array of my signal is complex. -- http://mail.python.org/mailman/listinfo/python-list
Re: any cherypy powred sites I can check out?
On 5/16/13 2:30 PM, Chris Angelico wrote: On Fri, May 17, 2013 at 4:17 AM, wrote: anyone? -- http://mail.python.org/mailman/listinfo/python-list You're firing off a bunch of minimal-content threads that ask other people to do work for you. I recommend you put a bit more thought into your posts, and show that you're willing to do a basic web search before you just ask a question :) He's also known on the Tcl newsgroup as Gavino; a Google search for "gavino tcl" will turn up some interesting hits. I also see that he's posting on comp.lang.perl as "Johannes Falcone." The common thread of his recent postings are subjects posed as questions, usually about various web frameworks, sometimes without even a single line in the message body. On the Tcl list it's AOLServer and NavServer. I'm not familiar with the Perl frameworks he's curious about. --Kevin -- Kevin Walzer Code by Kevin/Mobile Code by Kevin http://www.codebykevin.com http://www.wtmobilesoftware.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Please help with Threading
On 05/19/2013 05:46 PM, Dennis Lee Bieber wrote: On Sun, 19 May 2013 10:38:14 +1000, Chris Angelico declaimed the following in gmane.comp.python.general: On Sun, May 19, 2013 at 10:02 AM, Carlos Nepomuceno wrote: I didn't know Python threads aren't preemptive. Seems to be something really old considering the state of the art on parallel execution on multi-cores. What's the catch on making Python threads preemptive? Are there any ongoing projects to make that? With interpreted code eg in CPython, it's easy to implement preemption in the interpreter. I don't know how it's actually done, but one easy implementation would be "every N bytecode instructions, context switch". It's still done at a lower level than user code (N bytecode Which IS how the common Python interpreter does it -- barring the thread making some system call that triggers a preemption ahead of time (even time.sleep(0.0) triggers scheduling). Forget if the default is 20 or 100 byte-code instructions -- as I recall, it DID change a few versions back. Part of the context switch is to transfer the GIL from the preempted thread to the new thread. So, overall, on a SINGLE CORE processor running multiple CPU bound threads takes a bit longer just due to the overhead of thread swapping. On a multi-core processor, the effect is the same, since -- even though one may have a thread running on each core -- the GIL is only assigned to one thread, and other threads get blocked when trying to access runtime data structures. And you may have even more overhead from processor cache misses if the a thread gets assigned to a different core. (yes -- I'm restating the same thing as I had just trimmed below this point... but the target is really the OP, where repetition may be helpful in understanding) So what's the mapping between real (OS) threads, and the fake ones Python uses? The OS keeps track of a separate stack and context for each thread it knows about; are they one-to-one with the ones you're describing here? If so, then any OS thread that gets scheduled will almost always find it can't get the GIL, and spend time thrashing. But the change that CPython does intentionally would be equivalent to a sleep(0). On the other hand, if these threads are distinct from the OS threads, is it done with some sort of thread pool, where CPython has its own stack, and doesn't really use the one managed by the OS? Understand the only OS threading I really understand is the one in Windows (which I no longer use). So assuming Linux has some form of lightweight threading, the distinction above may not map very well. -- DaveA -- http://mail.python.org/mailman/listinfo/python-list
Re: Harmonic distortion of a input signal
killybear...@gmail.com wrote: One more question. Function np.argmax returns max of non-complex numbers ? Because FFT array of my signal is complex. You'll want the magnitudes of the complex numbers. Actually the squares of the magnitudes (assuming the data from the oscilloscope represents voltages), because you're after a ratio of powers. -- Greg -- http://mail.python.org/mailman/listinfo/python-list
Re: Harmonic distortion of a input signal
On 05/19/2013 07:36 PM, killybear...@gmail.com wrote: One more question. Function np.argmax returns max of non-complex numbers ? Because FFT array of my signal is complex. It'd be easier to track the thread if you actually replied to the message you're responding to, and also if you included some context. But I'll paste the latter in here: Terry Reedy said: > Compute the magnitude spectrum: >>> spect = abs(np.fft.fft(x)[:25]) >>> spect > array([ 0., 31.85194222, 0., 10.67342282, > 0., 6.47213595, 0., 4.69726931, > 0., 3.73254943, 0., 3.13762901, > 0., 2.7436023 , 0., 2.47213595, > 0., 2.28230601, 0., 2.15105461, > 0., 2.06487174, 0., 2.01589594, > 0.]) > Find the index of the maximum element: >>> np.argmax(spect) > 1 Notice that argmax's argument is the result of an abs() call. It's got real numbers representing the magnitude of the various complex numbers. -- DaveA -- http://mail.python.org/mailman/listinfo/python-list
Re: mutable ints: I think I have painted myself into a corner
Cameron Simpson wrote: It's an int _subclass_ so that it is no bigger than an int. If you use __slots__ to eliminate the overhead of an instance dict, you'll get an object consisting of a header plus one reference, which is probably about the size of an int. But you'll also need an int to put in that slot, so the total size will be about twice that of an int. Another approach would be to subclass array.array and give instances of it type integer and size 1. Together with empty __slots__, it will probably be a bit bigger than an int, but it might still be smaller than a custom object plus an int. If all of these are still too big, you might need to find some way of packing multiple instances into a single array.array. -- Greg -- http://mail.python.org/mailman/listinfo/python-list
Re: How to write fast into a file in python?
Carlos Nepomuceno wrote: >Python really writes '\n\r' on Windows. Just check the files. It actually writes \r\n, but it's not Python that's doing it. It's the C runtime library. And, of course, you can eliminate all of that by opening the file in binary mode open(name,'wb'). -- Tim Roberts, t...@probo.com Providenza & Boekelheide, Inc. -- http://mail.python.org/mailman/listinfo/python-list
How to run a python script twice randomly in a day?
hi, How to run a python script twice randomly in a day? Actually I want to run my script randomly in a day and twice only. Please help me.. how is it possible. Thanks -- http://mail.python.org/mailman/listinfo/python-list
Re: How to run a python script twice randomly in a day?
>How to run a python script twice randomly in a day? Actually I want to run > my script randomly in a day and twice only I can think of two basic approaches. One, use crontab or some other similar functionality to call it exactly twice. Two, use crontab or some other similar functionality to call it every minute, and add code to your script to execute exactly twice. Which are you preferring? -- http://mail.python.org/mailman/listinfo/python-list
Re: How to run a python script twice randomly in a day?
On 19May2013 20:54, Avnesh Shakya wrote: |How to run a python script twice randomly in a day? Actually | I want to run my script randomly in a day and twice only. Please | help me.. how is it possible. Do you mean "run twice a day, each at random times"? If so, do the obvious: at midnight, pick two random times. Sleep until the first time, run the script, sleep until the second time, run the script. There are various ways to do the sleeping and midnight bits; they're up to you. Enjoy, -- Cameron Simpson The ZZR-1100 is not the bike for me, but the day they invent "nerf" roads and ban radars I'll be the first in line..AMCN -- http://mail.python.org/mailman/listinfo/python-list
Re: Future standard GUI library
Terry Jan Reedy wrote: >> Do you think tkinter is going to be the standard python built-in gui >> solution as long as python exists? > > AT the moment, there is nothing really comparable that is a realistic > candidate to replace tkinter. FLTK? (http://www.fltk.org/index.php) -- ZeD -- http://mail.python.org/mailman/listinfo/python-list
Re: mutable ints: I think I have painted myself into a corner
On 19May2013 09:01, Peter Otten <__pete...@web.de> wrote:
| Cameron Simpson wrote:
|
| > TL;DR: I think I want to modify an int value "in place".
| >
| > Yesterday I was thinking about various "flag set" objects I have
| > floating around which are essentially bare "object"s whose attributes
| > I access, for example:
| >
| > flags = object()
| > flags.this = True
| > flags.that = False
| >
| > and then elsewhere:
| >
| > if flags.that:
| > do that ...
| >
| > Nice and readable, but I thought to myself: so bulky!
|
| Plus, it doesn't work:
Yeah, sorry. My "old" code was a trite subclass of object.
The new broken code is a subclass of int.
| > But setting up a flags object? What I _want_ to write is code like this:
| >
| > Flags = BitMask('this', 'that')
| >
| > # set default state
| > flags = Flags()
| > flags.this = False
| > flags.that = True
| > ... iterate over some options ...: flags.this = True
| >
| > and there's my problem. This would modify the int in place. There's
| > no way to do that. For the base type (int) this makes perfect sense,
| > as they're immutable.
| >
| > Before I toss this approach and retreat to my former "object"
| > technique, does anyone see a way forward to modify an int subclass
| > instance in place? (That doesn't break math, preferably; I don't
| > do arithmetic with these things but they are, after all, ints...)
|
| No, but you could make
|
| flags = Flags(this=False, that=True)
Yes, that is true. Flags would need to be a factory function computing
the corresponding bitmask value and then returning my new int, but
it would work. It still wouldn't let me go the whole way of modifying
the flags after instantiation.
Cheers,
--
Cameron Simpson
Carpe Daemon - Seize the Background Process
- Paul Tomblin
--
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Re: mutable ints: I think I have painted myself into a corner
On 20May2013 13:23, Greg Ewing wrote: | Cameron Simpson wrote: | >It's an int _subclass_ so that it is no bigger than an int. | | If you use __slots__ to eliminate the overhead of an | instance dict, you'll get an object consisting of a | header plus one reference, which is probably about the | size of an int. But you'll also need an int to put in | that slot, so the total size will be about twice that | of an int. Yeah, I was thinking I'd need to go that way. Thanks for the suggestion. | Another approach would be to subclass array.array and | give instances of it type integer and size 1. Together | with empty __slots__, it will probably be a bit bigger | than an int, but it might still be smaller than a | custom object plus an int. Really? Interesting. I thinik it crosses my "too baroque" threshold, but maybe not:-) | If all of these are still too big, you might need to | find some way of packing multiple instances into a | single array.array. Space isn't that real an issue at present; I'll keep that kind of approach in mind if it comes up. This really came up because I was feeling that the obvious object-with-boolean-attributes was terrbily wasteful for something that can be inplemented with a single int, in principle. Cheers, -- Cameron Simpson >>>How do you blip the throttle and wave? Do you blip it real high, then wave >>>before the revs drop back? >>Blip = right hand; Wave = left hand. Do both simultaneously. QED. >Doesnt this make the bike lurch forward thru the intersection? Not if the disk lock is in place... - Dean Woodward -- http://mail.python.org/mailman/listinfo/python-list
Re: Please help with Threading
On 18 May 2013 20:33, "Dennis Lee Bieber" wrote: > Python threads work fine if the threads either rely on intelligent > DLLs for number crunching (instead of doing nested Python loops to > process a numeric array you pass it to something like NumPy which > releases the GIL while crunching a copy of the array) or they do lots of > I/O and have to wait for I/O devices (while one thread is waiting for > the write/read operation to complete, another thread can do some number > crunching). Has nobody thought of a context manager to allow a part of your code to free up the GIL? I think the GIL is not inherently bad, but if it poses a problem at times, there should be a way to get it out of your... Way. -- http://mail.python.org/mailman/listinfo/python-list
