24.12.21 00:09, Guido van Rossum пише:
> Without decorator too (that was Lukasz’ idea). Why bother with the
> decorator (*if* we were to go there)?
It is errorprone.
Some library provide function foo() which returns an instance of private
type _Foo and people start using it as a type hint. A new version
converts foo() into a class. It is usually a safe backward compatible
change, except that now all type hints became wrong. "a: foo" now means
an instance of foo, not a callable which returns an instance of _Foo.
There are also issues with subclassing.
>>> foo = Callable[[int], str]
>>> class A(foo): ...
...
>>> def bar(x: int, /) -> str: pass
...
>>> class B(bar): ...
...
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: function() argument 'code' must be code, not str
There are also issues with subscripting:
>>> T = TypeVar('T')
>>> foo = Callable[[T], list[T]]
>>> list[foo][int]
list[typing.Callable[[int], list[int]]]
>>> def bar(x: T, /) -> list[T]: pass
...
>>> list[bar][int]
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: There are no type variables left in list[__main__.bar]
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