On 2007-05-23, Bruno Desthuilliers <[EMAIL PROTECTED]> wrote:
> 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:
An immutable object would have given the same behaviour in this case
class A(object):
def __init__(self, val = ()):
self.val=val
obj1 = A()
obj2 = A()
print obj1 is obj2 # False
print obj1.val is obj2.val # True
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