Re: Events: The Python Way
On 2007-07-29, at 02:34, David Wilson wrote: > Hi there, > > Python has no built-in way of doing this. You may consider writing > your own class if you like this pattern (I personally do): > > class Event(object): > def __init__(self): > self.subscribers = set() ... > def __isub__(self, subscriber): > self.subscribers.pop(subscriber) > return self A slight typo there. For sets s.pop() returns an arbitrary element and s.remove(x) or s.discard(x) removes the element x from the set s. For the OP: remove raises an exception if x is not in the set, discard does not. -- [ [EMAIL PROTECTED] <*> Antti Rasinen ] "The music of rebellion makes you wanna rage But it's made by millionaires who are nearly twice your age" -- http://mail.python.org/mailman/listinfo/python-list
Re: Detecting __future__ features
On 2007-07-30, at 15:29, Steven D'Aprano wrote: > How would one tell at runtime if a particular feature has been > enabled by > the "from __future__ import thing" statement? > > (I don't especially care whether the feature in question has been > enabled > via an explicit call to import, or because it has become the default.) > > Is there any general mechanism? You probably have to care about imports vs. language defaults. But it's not very difficult. For imports you can use __future__ to help you. If your namespace contains a feature you want to check for and it is identical to the same feature in __future__, then the code has used from __future__ import feature. You could probably try something like this: import __feature__ feature = "division" if globals().get(feature, None) == __future__.__dict__[feature]: print "Bingo!" You can probably figure out how to use sys.version_info to check whether the current Python version is higher than the one specified in a feature line: import __future__ import sys if sys.version_info >= __future__.division.mandatory: print "Bingo! Two in a row!" Check the __future__ docstrings for more information. -- [ [EMAIL PROTECTED] <*> Antti Rasinen ] This drone-vessel speaks with the voice and authority of the Ur-Quan. -- http://mail.python.org/mailman/listinfo/python-list
Re: removing redundant elements in a dictionary
On 2007-08-01, at 06:50, Astan Chee wrote:
Hi,
I have a dictionary which looks something like this:
elem = {"co":[1,2,3],"cp":[3,2,1],"pp":[5,6,7],"cl":[1,2,3],"qw":
[6,7,8],"qa":[8,7,6]}
what Im trying to do is find all keys in the list that have the
same value and delete those (except one); thereby removing all
redundant keys so that the above dict will look like this:
elem = {"co":[1,2,3],"pp":[5,6,7],"qa":[8,7,6]}
my code so far looks like this:
for out1 in elem.keys():
for out2 in elem.keys():
if out1 != out2:
elem[out1].sort()
elem[out2].sort()
if elem[out1] == elem[out2]:
del elem[out1]
This returns in a KeyError exception when sorting. What am I
missing here?
Consider a dict {'a': [1], 'b': [1], 'c': [1]}.
First time we reach the innerloop, out1 == 'a'. Then we iterate over
the list ['a', 'b', 'c'].
'a' is skipped. At 'b', we remove 'a' from the dictionary. And then
it all goes wrong.
The last time we go through the inner loop, out1 is still 'a' -- an
element which does not exist in the dictionary anymore. Then your
attempts to reference it fail at both the sorting and comparison
stages. You should break out of the inner loop immediately after
you've deleted the item or delete out2 instead..
Furthermore, the algorithm is somewhat inefficient due to the fact
that it sorts the lists O(n^2) times when you only need to do them n
times. If your data allows it, you might like to use sets instead of
lists. This would avoid the need to sort the lists.
However, here is a very quick version that works in my tests:
for out_list in elem.values():
out_list.sort()
for out1 in elem.keys():
for out2 in elem.keys():
if out1 != out2 and elem[out1] == elem[out2]:
del elem[out1]
break
There are probably several ways to improve on that, however.
--
[ [EMAIL PROTECTED] <*> Antti Rasinen ]
"Pay the man his wage, he's making paper to fuel the Information Age."
--
http://mail.python.org/mailman/listinfo/python-list
Re: Use variable in regular expression
On 2007-08-02, at 13:43, [EMAIL PROTECTED] wrote: > I know I can use a variable in regular expressions. I want to use a > regex to find something based on the beginning of the string. I am > using yesterday's date to find all of my data from yesterday. > Yesterday's date is 20070731, and assigned to the variable > "yesterday_date". I want to loop thru a directory and find all of the > yesterday's data ONLY IF the feature class has the date at the > BEGINNING of the filename. > > ... > I don't want the one's that start with "Copy". I can't figure out the > syntax of inserting the "^" into the regex. I've tried all of the > following, with no luck: > > re.compile(^yesterday_date) > re.compile(r'^yesterday_date') > re.compile(r'^[yesterday_date]') > re.compile(r'[^yesterday_date]') The first one is a syntax error (^ outside a string means the xor- operation). The rest are just strings containing the _string_ 'yesterday_date' and not the value of the variable. So you need to do some string formatting(* search_str = '^%s' % yesterday_date # I'm assuming yesterday_date is a string. re.compile(search_str) *) http://docs.python.org/lib/typesseq-strings.html -- [ [EMAIL PROTECTED] <*> Antti Rasinen ] This drone-vessel speaks with the voice and authority of the Ur-Quan. -- http://mail.python.org/mailman/listinfo/python-list
Re: Question about properties.
> Hi, > > i read in a book the following code snippet that is dealing with > properties: > > class ProtectAndHideX(object): > def __init__(self, x): > assert isinstance(x, int), '"x" must be an integer!"' > self.__x = ~x > > def get_x(self): > return ~self.__x > > x = property(get_x) > > > Can anyone please help me understand what the symbol "~" does here ?? My guess is that the example tries to show that it does not matter how the property computes the value. You can -- if you want -- to store integers as their bit-inverted versions (the ~ operator) and then do the conversion when getting the property value. Assume you initialized the object with ProtectAndHideX(4). Outside the object you don't have access to the original __x. And! Even if you changed the name of the variable name to y, you'd have hidden_x.y == -5 instead of 4. The example is very contrived. There might be some security related cases where you need to hide what you store in memory, though. (Hopefully they do more than just invert the bits! :) NB: I don't know what the original author was thinking here -- my telepathy isn't what it used to be. -- [ Antti Rasinen <*> [EMAIL PROTECTED] ] -- http://mail.python.org/mailman/listinfo/python-list
