19.06.21 06:30, wyz2...@163.com пише:
> Python raises TypeError when NotImplemented is returned from __add__,
> __invert__ etc. and __radd__ etc. aren't available.
> However, this disallows the customization of error messages. For example, in
> Python 3.8, __float__ etc. were removed from complex to allow methods like
> __rfloat__. But this makes abs(z) undiscoverable for many users. The original
> error message is very helpful.
> I suggest to make a way for this usage. Maybe NotImplementedType can accept
> *args, and NotImplemented can be callable, equal to __init__:
>
>>>> class A:
> def __add__(self, other):
> return NotImplemented # Just like before
> def __neg__(self, other):
> return NotImplemented(f'bad operand type for unary -:
> {type(self).__name__!r}; use ~ to invert') # <--
> def __invert__(self):
> return ~5
>>>> a = A()
>>>> a + 2
> TypeError: unsupported operand type(s) for +: 'A' and 'int'
>>>> -a
> TypeError: bad operand type for unary -: 'A'; use ~ to invert
>>>> ~a
> -6
NotImplemented is a singleton. And all code which tests for
NotImplemented does it by checking identity. Returning any other object
instead of the NotImplemented would not work.
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