Siah a écrit :
> Ready to go insane here. Class A, taking on a default value for a
> variable. Instantiating two separate objects of A() gives me a shared
> val list object. Just see the example bellow:
>
>
> class A(object):
> def __init__(self, val=[]):
> self.val=val
>
> obj1 = A()
> obj2 = A()
>
> print obj1 is obj2 # False - as expected
> print obj1.val is obj2.val # True! - Why... oh god WHY
>
>
> -----------
> Using python 2.4. Is this a bug with this version of python? How can I
> trust the rest of the universe is still in place? Could she still like
> me? Many questions I have. Lets start with the python problem for now.
This is a FAQ. Default arguments are only evaled once - when the def
statement is evaled (which is usually at import time). The solution is
simple: don't use mutable objects as default arguments:
class A(object):
def __init__(self, val=None):
if val is None:
val = []
self.val=val
FWIW, do you really believe such a 'bug' would have stayed unnoticed ?-)
Else, the rest of the universe seems to be in place, and I don't know if
she'll still like you if she learn you didn't read the FAQ before
posting !-)
HTH
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