On Apr 17, 8:56 am, "matthewperpick" <[EMAIL PROTECTED]> wrote:
> Check out this toy example that demonstrates some "strange" behaviour
> with keyword arguments and inheritance.
>
> =================================
>
> class Parent:
> def __init__(self, ary = []):
> self.ary = ary
>
> def append(self):
> self.ary.append(1)
>
> class Child(Parent):
> def __init__(self):
> Parent.__init__(self)
> self.append()
>
> def main():
> a = Child()
> print a.ary
> b = Child()
> print b.ary
>
> main()
>
> =====================================
>
> You would think the output of this program would be [1], [1]. But
> strangely enough the output is [1,], [1,1]. I suppose that the
> Parent.__class__ object is only created once and thus the keyword
> argument always refers to the same thing, but I don't know. I have a
> very rudimentary understading of python's guts, but I would still call
> the behaviour unexpected. Or perhaps I should rtfm?
>
> Any thoughts would be much appreciated. Thanks.
A slight modification of init-ing the parent can give you the expected
output.
class Child(Parent):
def __init__(self):
Parent.__init__(self, [])
self.append()
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