[Python-Dev] Possible bug in class-init, lookin for mentors

[Paul Moore]

This is correct behaviour. I would suggest that you post this to
python-list for a full discussion of what's going on here, but
basically the default value for argument bar of __init__ is created at
class creation time, and then reused for every instance. This is a
common mistake made by newcomers, using mutable default arguments for
functions (or methods).

A google search for "python mutable default argument" should find you
some useful explanations of what's going on.

Cheers,
Paul

On 21 April 2017 at 10:47, Justus Schwabedal <jschwabedal at gmail.com> wrote:
> Hi everyone,
>
> I possibly found a bug in class __init__ and would like to fix it.  So I'm
> looking for a mentor to help me.
>
> `class Foo:
>     def __init__(self, bar=[]):
>         self.list = bar
>
> spam_1 = Foo()
> spam_2 = Foo()
>
> spam_1.list.append(42)
> print(spam_2.list)`
>
> At least I think it's a bug.  Maybe it's a feature..
>
> Best Regards, Jus
>
>
>
>
>
> --
> Justus Schwabedal
>
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