classes and list as parameter, whats wrong?

[Dirk Zimmermann]

Hi!

I have a problem in a program. And I don't understand what is going on.
I can code something, that the "error" doesn't occur anymore. But I
still don't know the reason and this is unsatisfactory: Did I understood
something wrong or is there a bug? To make it short, I boiled down the
program to the crucial part.  It looks like this:

--- START 
#!/usr/bin/env python

class cClass:
""" Base class to handle playlists, i.e. the files, the name, etc. """
def __init__(self, LL=[]):
self.list=LL
def addFile(self,L):
self.list.append(L)

def main():
l1 = ['a','b','c']
lNames=['n1','n2','n3']
for name in lNames:
objC=cClass()
for each in l1:
objC.addFile(each)
print objC.list
del objC

if __name__ == "__main__":
main()
--- END 

If I start it, I get the following output:

['a', 'b', 'c']
['a', 'b', 'c', 'a', 'b', 'c']
['a', 'b', 'c', 'a', 'b', 'c', 'a', 'b', 'c']


Why does this list grow? I thought, with every new instance the list LL
is set to []?

How can bring light in this?


Best,
Dirk


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Re: classes and list as parameter, whats wrong?

[Dirk Zimmermann]

Thanks for your help.

* James <[EMAIL PROTECTED]> [2005-08-26 11:42]:
> No, the default paramter LL is only ever created once, not
> reinitialised every time the constructor is called - this is quite a
> common gotcha!

But still, it is not absolutely clear for me, what is going on. So, at
least just for my understanding: The parameter LL is created just once
for the whole class and not for the object (because I del the object
explicitly, which should destroy the object)?

Thanks,
Dirk


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Re: classes and list as parameter, whats wrong?

[Dirk Zimmermann]

Thanks to everyone! I think I understand the things behind this
behaviour, now.

And as the life goes: Today I found the description of my "problem" in
the Python Tutorial! I think I should read it more often, more
carefully:-)


Best,
Dirk

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How to kill/stop a Thread?

[Dirk Zimmermann]

Hi,

I like to do the following: Via http I get a stream of data and I like
to store this data with a python program. So what I need is to start the
downloading and to stop it after a given time. My aproach was to use:
urllib.urlretrieve("ULR","FILENAME")

It is fine! But how to stop the retrieving? Because it is a constant
stream of data there is no natural end. So I thought I use
treading.Thread to do it:

def retr():
urllib.urlretrieve("URL","FILENAME")

t=threading.Thread(target=retr)
t.start()

It's fine! The data is downloaded and I'm back in my program to do some
other stuff. BUT: I cannot stop the download. How can I achieve this?
(Another way of solution (w/o threading) would also helpful, of course!)


Thanks for your help,
Dirk



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