On Wed, Jul 9, 2014 at 3:54 AM, Chris Angelico <ros...@gmail.com> wrote:
>>>> class X:
> def __eq__(self, other):
> if self is other:
> print("Comparing against self - I am me!")
> return True
> print("Comparing against",other,"-",id(other))
> return False
> def __hash__(self):
> return 0
>
>>>> d[X()]
> Comparing against nan - 18777952
> Comparing against nan - 19624864
> Comparing against nan - 18776272
> Traceback (most recent call last):
> File "<pyshell#20>", line 1, in <module>
> d[X()]
> KeyError: <__main__.X object at 0x016B40D0>
Better example: Subclass float, then it can actually *be* a nan.
>>> class NoisyFloat(float):
def __eq__(self, other):
print("Comparing",id(self),"against",id(other))
return super().__eq__(other)
def __hash__(self):
return super().__hash__()
>>> d[NoisyFloat("nan")]
Comparing 23777152 against 18777952
Comparing 23777152 against 19624864
Comparing 23777152 against 18776272
Traceback (most recent call last):
File "<pyshell#35>", line 1, in <module>
d[NoisyFloat("nan")]
KeyError: nan
That's comparing nan==nan three types with four different nans.
ChrisA
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