Re: Class Help
On Sat, 2005-10-01 at 18:58 -0400, Ivan Shevanski wrote: > To continue with my previous problems, now I'm trying out classes. But I > have a problem (which I bet is easily solveable) that I really don't get. > The numerous tutorials I've looked at just confsed me.For intance: > > >>>class Xyz: > ... def y(self): > ... q = 2 > ... > >>>Xyz.y() > Traceback (most recent call last): > File "", line 1, in ? > TypeError: unbound method y() must be called with Xyz instance as first > argument > (got nothing instead) > > > So. . .What do I have to do? I know this is an extremley noob question but I > think maybe if a person explained it to me I would finally get it =/ When you define a class, say Xyz, your are defining your own type. Say that Person is a class. And person has a method walk(): class Person: def walk(self): ... now to use the Person class, you need to create an instance of it. You can't just say Person.walk() because Person is a "class"ification, not a real object. You need an instance of person. jane = Person() This creates a new person called "jane". "jane" is an instance of the class Person. >>> jane <__main__.Person instance at 0x2c723710> Now we can tell jane to walk: jane.walk() So what the error is telling you (in a bit confusing way if you're a newbie) is that you are calling a method y() but you have not created an instance of your Xyz class to do y(). Or, to use my analogy, you are telling Person to walk, but you can't make Person walk, you have to create a person, jane, and have jane walk. Hope this helps, but I recommend you read a good intro to object-oriented programming. -a -- http://mail.python.org/mailman/listinfo/python-list
Re: "no variable or argument declarations are necessary."
> egold = 0:
> while egold < 10:
> if test():
> ego1d = egold + 1
>
Both pylint and pychecker pick this up. I wrapped the code in a
function (to prevent importing from running in an infinite loop) and ran
both pylint and pychecker:
plyint: W: 5:myfunc: Unused variable 'ego1d'
pychecker: test.py:4: Local variable (ego1d) not used
I make a habit to run pylint or pychecker on my code often. They pick
up a lot of stuff like unused variables, etc.
But you can also do this:
/* initialize variables i'm gonna use */
int vara = 0;
int varb = 0;
while (vara < 10) {
varb = vara + 1;
}
So we can make a similar mistake in C if you type the wrong (declared)
variable name. Moreover, "gcc -Wall" did not report the "unused"
variable so it might be even more difficult to track down the problem.
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Re: "no variable or argument declarations are necessary."
On Tue, 2005-10-04 at 11:43 -0700, Paul Rubinhttp: wrote:
> What's the big deal? Perl has an option for flagging undeclared
> variables with warnings ("perl -w") or errors ("use strict") and Perl
> docs I've seen advise using at least "perl -w" routinely. Those
> didn't have much impact. Python already has a "global" declaration;
> how does it de-Pythonize the language if there's also a "local"
> declaration and an option to flag any variable that's not declared as
> one or the other?
I would be happy with a "local" option. e.g.
def myfunc():
local spam = ...
local eggs = ...
global juice
breakfast = juice + spam + eggs # raises an exception (undeclared
breakfast)
What I'm *afraid* of is:
def myfunc(MyClass myparam):
int spam = 6
str eggs
# etc
i.e. typed declarations and type checking. This would annoy the heck
out of me.
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Re: Jargons of Info Tech industry
[Removed X-posting] On Tue, 2005-10-04 at 17:14 +, Roedy Green wrote: > On Tue, 23 Aug 2005 08:32:09 -0500, l v <[EMAIL PROTECTED]> wrote or quoted : > > >I think e-mail should be text only. > > I disagree. Your problem is spam, not HTML. Spam is associated with > HTML and people have in Pavlovian fashion come to hate HTML. > > But HTML is not the problem! And guns don't kill people: people kill people! Seriously though, plain-text is just plain [n]etiquette (for most newsgroups/mailing lists (at least the technical ones)). Follow the rules and avoid becoming a social outcast. If your particular forum allows/encourages HTML then away! ( This post is neither x-posted, HTML-ized, closed-captioned nor simulcast in Spanish or HD ) -- http://mail.python.org/mailman/listinfo/python-list
how to keep collection of existing instances and return one on instantiation
I couldn't think of a good subject..
Basically, say I have a class
class Spam:
def __init__(self, x):
self.x = x
then if I create two instances:
a = Spam('foo')
b = Spam('foo')
a == b # False
What I *really* want is to keep a collection of all the Spam instances,
and if i try to create a new Spam instance with the same contructor
parameters, then return the existing Spam instance. I thought new-style
classes would do it:
class Spam(object):
cache = {}
def __new__(cls, x):
if cls.cache.has_key(x):
return cls.cache[x]
def __init__(self, x):
self.x = x
self.cache[x] = self
a = Spam('foo')
b = Spam('foo')
Well, in this case a and b are identical... to None! I assume this is
because the test in __new__ fails so it returns None, I need to then
create a new Spam.. but how do I do that without calling __new__ again?
I can't call __init__ because there's no self...
So what is the best/preferred way to do this?
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Re: how to keep collection of existing instances and return one on instantiation
On Wed, 2005-10-05 at 12:56 -0400, Jonathan LaCour wrote:
> Oops, you forgot to return object.__new__(cls, x) in the case the
> object isn't in the cache. That should fix it.
Ahh, that did it. I didn't even think of calling object...
so the new class looks like:
class Spam(object):
cache = {}
def __new__(cls, x):
if cls.cache.has_key(x):
return cls.cache[x]
else:
new_Spam = object.__new__(cls, x)
cls.cache[x] = new_Spam
return new_Spam
def __init__(self, x):
self.x = x
a = Spam(2)
b = Spam(2)
a == b # => True
id(a) == id(b) # => True
Thanks for all your help.
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Re: how to keep collection of existing instances and return one on instantiation
On Wed, 2005-10-05 at 18:28 +0200, Diez B. Roggisch wrote: > Use the BORG-pattern. See > > > http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/66531 > > Together with your caching, that should do the trick. > I looked at the Borg Pattern, but I don't think it was exactly what I want. The Borg patten appears to be if you want multiple instances that point to the same "data". What I wanted is multiple calls to create a new object with the same parameters points to the "original" object instead of creating a new one. -- http://mail.python.org/mailman/listinfo/python-list
Re: how to keep collection of existing instances and return one on instantiation
On Wed, 2005-10-05 at 12:56 -0400, Jonathan LaCour wrote:
> > class Spam(object):
> > cache = {}
> > def __new__(cls, x):
> > if cls.cache.has_key(x):
> > return cls.cache[x]
> > def __init__(self, x):
> > self.x = x
> > self.cache[x] = self
> >
> > a = Spam('foo')
> > b = Spam('foo')
> >
> > Well, in this case a and b are identical... to None! I assume this is
> > because the test in __new__ fails so it returns None, I need to then
> > create a new Spam.. but how do I do that without calling __new__
> > again?
> > I can't call __init__ because there's no self...
> >
> >
>
> Oops, you forgot to return object.__new__(cls, x) in the case the
> object isn't in the cache. That should fix it.
Okay, one more question... say I then
c = Spam('bar')
del a
del b
I've removed all references to the object, except for the cache. Do I
have to implement my own garbage collecting is or there some "magical"
way of doing this within Python? I pretty much want to get rid of the
cache as soon as there are no other references (other than the cache).
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Re: how to keep collection of existing instances and return one on instantiation
On Wed, 2005-10-05 at 19:37 +0200, Diez B. Roggisch wrote: > > What I wanted is multiple calls to create a new object with the same > > parameters points to the "original" object instead of creating a new > > one. > > Read the comments. What you say is essentially the same - the data > matters, after all. What do you care if there are several instances > around? > > Diez In my case it matters more that the objects are the same. For example I want set([Spam(1), Spam(2), Spam(3)]).intersect(set([Spam(1), Spam(2)]) to contain two items instead of 0. For this and many other reasons it's important that Spam(n) is Spam(n). -- http://mail.python.org/mailman/listinfo/python-list
Re: how to keep collection of existing instances and return one on instantiation
On Wed, 2005-10-05 at 19:24 +0200, Peter Otten wrote: > Use a weakref.WeakValueDictionary as the cache instead of a normal > dict. > > Peter Thanks for the reference to the weakref module. Until now I've never had a use for it, but it sounds like what I'm looking for. -m -- http://mail.python.org/mailman/listinfo/python-list
Re: Let My Terminal Go
On Mon, 2005-10-10 at 22:58 -0700, [EMAIL PROTECTED] wrote: > Hello, > > A user of my application points me to a behavior in gVim, > the text editor, that I would like to implement in my > application. > > When gVim is launched from a shell terminal, it completely > frees the terminal. You can continue to use the terminal for > whatever purpose you wish, including closing and exiting it, > without any effect on the running gVim instance. > > How do I implement this in my application written in python? > I would like to believe it does not involve me forking my > application in a new process. Maybe there is signal I can > send to the operating system to achieve this, right? gvim forks. Why do you want to avoid it? import os, sys pid = os.fork() if pid !=0: # exit parent sys.exit(0) # child continues -- http://mail.python.org/mailman/listinfo/python-list
Re: piping out binaries properly
On Wed, 2005-10-12 at 00:16 -0400, Mike Meyer wrote: [...] > It's not normal to write binary content to stdout - you normally write > it to a file. Open the file with open(name, 'wb') to write binaries. > It is interesting that as a "Unix consultant" you should make that claim. Especially since >>> sys.stdout ', mode 'w' at 0x2aac9198> Indeed there would be a lot of broken Unix systems out there if that were not the case. As for the OP, you may want to check how stdout is opened on your system. In Windows there are two "write" modes for files, 'w', and 'wb' where apparently 'w' is text mode and 'wb' is binary. You may want to check what mode your stdout is in. I don't have a Windows box handy right now to verify. > There doesn't appear to be any way to retroactively change the mode on > a file. Which is probably a good thing. > > Mike Meyer <[EMAIL PROTECTED]> http://www.mired.org/home/mwm/ > Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information. -- http://mail.python.org/mailman/listinfo/python-list
Re: grep
On Tue, 2005-10-25 at 06:45 +, David Isaac wrote: > What's the standard replacement for the obsolete grep module? AFAIK there never was a "grep" module. There does, however exist a deprecated "regex" module: >>> import regex __main__:1: DeprecationWarning: the regex module is deprecated; please use the re module -- http://mail.python.org/mailman/listinfo/python-list
Re: pickle
On Mon, 2005-10-24 at 23:55 -0700, Shi Mu wrote:
> I got a sample code and tested it but really can not understand the
> use of pickle and dump:
>
> >>> import pickle
> >>> f = open("try.txt", "w")
> >>> pickle.dump(3.14, f)
> >>> pickle.dump([1,2,3,4], f)
> >>> f.close()
The pickle module "serializes" python objects. You can "dump" a python
object that can later be loaded:
>>> x = complex(2,3.5)
>>> f = open("cnumber.pickle", "w")
>>> import pickle
>>> pickle.dump(x, f)
>>> f.close()
>>> y = pickle.load(file("cnumber.pickle", "r"))
>>> y
(2+3.5j)
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Re: I Need Motivation Part 2
On Fri, 2005-11-04 at 17:06 +0100, Magnus Lycka wrote: > If Python appears more complex > than C++, you must be using a really weird approach. Or a really weird editor ;-) -m > -- http://mail.python.org/mailman/listinfo/python-list
Re: strip not working on strings?
On Sun, 2005-11-13 at 13:16 -0800, [EMAIL PROTECTED] wrote:
> I'm using Python 2.3.5 and when I type the following in the interactive
> prompt I see that strip() is not working as advertised:
>
> >>>s = 'p p:p'
> >>>s.strip(' :')
> 'p p:p'
>
> Is this just me or does it not work? I want to get rid of all ' ' and
> ':' in the string. I've checked the doc and from what I can tell this
> is what strip() is supposed to do. Thanks for any help.
>
According to my docs it says "Return a copy of the string with the
leading and trailing characters removed." There are no leading or
trailing spaces or colons in 'p p:p'.
What your probably looking for is the .replace() method.
-m
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Re: is parameter an iterable?
On Tue, 2005-11-15 at 11:01 -0800, py wrote: > I have function which takes an argument. My code needs that argument > to be an iterable (something i can loop over)...so I dont care if its a > list, tuple, etc. So I need a way to make sure that the argument is an > iterable before using it. I know I could do... > > def foo(inputVal): > if isinstance(inputVal, (list, tuple)): > for val in inputVal: > # do stuff > > ...however I want to cover any iterable since i just need to loop over > it. > > any suggestions? > You could probably get away with if hasattr(inputVal, '__getitem__') -- http://mail.python.org/mailman/listinfo/python-list
Re: Problems with os.system
On Fri, 2005-09-02 at 13:45 -0700, alexLIGO wrote: > Hi, > > I am trying to run a python script that executes several other programs > on the bash (under linux) and reads some of the output of those > programs. This works fine for a couple of os.system() calls, but then > it does not work anymore. os.system() returns always -1, but when > executing exactly the same program directly on the linux-bash it works! > > Could this be a memory problem? It happens when there is much data > stored in a python list. How can I check the memory usage in my python > script? Can I force python to execute the program on the bash? What can > I do? Are you trying to read the output (stdout) of the program? If so you should be using os.popen() not os.system(). -- http://mail.python.org/mailman/listinfo/python-list
Re: FTP status problems. (Again)
On Fri, 2005-09-16 at 19:27 -0700, Nainto wrote:
> Hello, I have posted before about trying to find the status of an FTP
> uplaod but couldn't get anything to work. After some more searching I
> found
> http://groups.google.com/group/comp.lang.python/browse_thread/thread/76be9a994547db4/91917c906cdc04d4?q=ftp+progress&rnum=1#91917c906cdc04d4
> but it does not seem to work because it just uploads the file and does
> not print a . onto the screen. HEre is the code I have when I'm using
> the code from that link.
> import ftplib
> import os
> class dot_FTP(ftplib.FTP):
> def storbinary(self, cmd, fp, blocksize=8192):
> self.voidcmd('TYPE I')
> conn = self.transfercmd(cmd)
> while 1:
> buf = fp.read(blocksize)
> if not buf: break
> conn.send(buf)
> sys.stdout.write('.')
> sys.stdout.flush()
> conn.close()
> return self.voidresp()
>
>
> ftp = ftplib.FTP("FTPADDRESS")
> ftp.login("user","pass")
> file = "/file"
> ftp.storbinary("STOR " + file, open(file, "rb"), 1024)
> ftp.quit()
> Does anyone know why this is not working? IS there any other way to
> find out when a chunc has been sent or the bytes uploaded of a file?
> Thanks.
>
... and I haven't tried this myself, but you should be able to subclass
the builtin file object and prepare your own read() method. Something
like
class ProgressFile(file):
def read(self, size = None):
print '.',
if size is not None:
return file.read(self, size)
else:
return file.read()
May need some tweaking.. then store the file as
ftp.storbinary("STOR " + file, ProgressFile(file, "rb"), 1024)
Give it a try..
-m
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Re: FTP status problems. (Again)
On Sat, 2005-09-17 at 04:42 +, marduk wrote:
>
> ... and I haven't tried this myself, but you should be able to subclass
> the builtin file object and prepare your own read() method. Something
> like
>
> class ProgressFile(file):
>
> def read(self, size = None):
> print '.',
>
> if size is not None:
> return file.read(self, size)
> else:
> return file.read()
>
> May need some tweaking.. then store the file as
>
> ftp.storbinary("STOR " + file, ProgressFile(file, "rb"), 1024)
>
> Give it a try..
>
> -m
>
I corrected some errors and made some modifications to my previous post:
class ProgressFile(file):
def read(self, size = None):
from sys import stdout
if size is not None:
buff = file.read(self, size)
if buff:
stdout.write('.')
else:
stdout.write('\n')
return buff
else:
buff = ''
while True:
new_str = file.read(self, 1024)
stdout.write('.')
if new_str:
buff = buff + new_str
else:
stdout.write('\n')
break
return buff
if __name__ == '__main__':
import sys
fname = sys.argv[1]
f = ProgressFile(fname)
f.read()
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Re: What is "self"?
On Thu, 2005-09-22 at 21:36 -0400, Wayne Sutton wrote: > OK, I'm a newbie... > I'm trying to learn Python & have had fun with it so far. But I'm having > trouble following the many code examples with the object "self." Can > someone explain this usage in plain english? "self" references the object itself. It's usually also called "this" on other languages (C++ & Java I believe). In Python, when you define a class method, the reference to the object is passed explicitly rather than implicitly. Also, the name "self" is used by convention. You could use any name if you wanted, but if you want other people to understand your code then use "self". Is that plain English enough? -- http://mail.python.org/mailman/listinfo/python-list
Re: How to pop random item from a list?
On Thu, 2006-03-09 at 21:59 -0800, flamesrock wrote: > Hi, > > It's been a while since I've played with python. > > My question is... whats the best way to pop a random item from a list?? import random # ... item = mylist.pop(random.randint(0,len(mylist))) -- http://mail.python.org/mailman/listinfo/python-list
