[issue3816] __newobj__ pickle feature is not documented

[Christian Heimes]

Christian Heimes <lists at cheimes.de> added the comment:

Christian Heimes wrote:
> Christian Heimes <lists at cheimes.de> added the comment:
> 
> Alexandre Vassalotti wrote:
>> Alexandre Vassalotti <alexandre at peadrop.com> added the comment:
>>
>> Could explain me how this feature could be used, other than for
>> providing the efficient and backward-compatible pickling mechanism for
>> new-style classes?
> 
> The feature makes it easy to write __reduce__ methods for subclasses of 
> builtins. Take this example:
> 
> def __newobj__(cls, *args):
>      return cls.__new__(cls, *args)
> 
> class mydict(dict):
>      def __reduce__(self):
>          state = (dict(self), self.__dict__)
>          return (__newobj__, (self.__class__,), state)

Of course one has to provide a __setstate__ method, too.

     def __setstate__(self, state):
         dict.update(self, state[0])
         self.__dict__.update(state[1])

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue3816>
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