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Re: Making unhashable object

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  Re: Making unhashable object Jean-Michel Pichavant <jeanmichel@sequans.com> - 2013-02-19 14:44 +0100

#39220 — Re: Making unhashable object

----- Original Message -----
> I am trying to define a class whose instances should not be hashable,
> following:
> http://docs.python.org/2/reference/datamodel.html#object.__hash__
> 
> class A:
>     def __init__(self,a):
>         self.value=a
>     __hash__=None
>     
> 
> Then:
> 
> >>> a=A(3)
> >>> hash(a)
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> TypeError: 'NoneType' object is not callable
> >>> hash([2])
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> TypeError: unhashable type: 'list'
> 
> I would expect the same error in both case and the error is confusing
> in the first case. What's the proper way of making an object non
> hashable?
> 
> Olive

Try

class A:
  def __hash__(self):
    raise TypeError("unhashable type: '%s'" % self.__class__.__name__)

JM


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