Serhiy Storchaka <[email protected]> added the comment:
It does not have a use case of T[int] in mind. It is an implementation detail
which simplifies the code, makes runtime checks more strict and makes
types.GenericAlias more similar to typing._GenericAlias.
For example, currently:
>>> A = List[T]
>>> B = list[T]
>>> A[None]
typing.List[NoneType]
>>> B[None]
list[None]
>>> A['X']
typing.List[ForwardRef('X')]
>>> B['X']
list['X']
With the proposed change:
>>> B[None]
list[NoneType]
>>> B['X']
list[ForwardRef('X')]
Meanless expressions like A[42], A[Final], A[Final[int]], A[ClassVar],
A[ClassVar[int]], etc which are silently accepted will now be errors.
The code simplification (especially for the C code) is my primary goal, and the
rest is a nice side effect. It is possible to add more strict runtime checks
and conversions without making TypeVar and ParamSpec subscriptable, but the
code will not be so simple.
----------
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Python tracker <[email protected]>
<https://bugs.python.org/issue44796>
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