[Python-Dev] About [].append == [].append

[INADA Naoki]

2018年6月21日(木) 20:27 Jeroen Demeyer <J.Demeyer at ugent.be>:

> Currently, we have:
>
>  >>> [].append == [].append
> False
>
> However, with a Python class:
>
>  >>> class List(list):
> ...     def append(self, x): super().append(x)
>  >>> List().append == List().append
> True
>
> In the former case, __self__ is compared using "is" and in the latter
> case, it is compared using "==".
>
> I think that comparing using "==" is the right thing to do because "is"
> is really an implementation detail.


I think "is" is correct because "bound to which object" is essential for
bound (instance) methods.


Consider
>
>  >>> (10000).bit_length == (10000).bit_length
> True
>  >>> (10000).bit_length == (10000+0).bit_length
> False
>

I'm OK for this difference.
This comparison is what people shouldn't do, like 'id(10000) == id(10000+0)'


> I guess that's also the reason why CPython internally rarely uses "is"
> for comparisons.
>
> See also:
> - https://bugs.python.org/issue1617161
> - https://bugs.python.org/issue33925
>
> Any opinions?
>

I think changing this may break some tricky code.
Is it really worth enough to change?


>
>
> Jeroen.
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