19.06.21 06:30, wyz23x2@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.