New submission from Serhiy Storchaka <storchaka+cpyt...@gmail.com>:
It works only with simple types >>> class X(Annotated[list, 'annotation']): pass ... But not with type aliases >>> class X(Annotated[List[int], 'annotation']): pass ... Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: _GenericAlias.__init__() takes 3 positional arguments but 4 were given >>> class X(Annotated[list[int], 'annotation']): pass ... Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: GenericAlias expected 2 arguments, got 3 And even if the original type is not subclassable, the error message is not always clear: >>> class X(Annotated[Union[int, str], 'annotation']): pass ... Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: _GenericAlias.__init__() takes 3 positional arguments but 4 were given >>> class X(Annotated[int | str, 'annotation']): pass ... Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: _GenericAlias.__init__() takes 3 positional arguments but 4 were given ---------- components: Library (Lib) messages: 400021 nosy: gvanrossum, kj, serhiy.storchaka priority: normal severity: normal status: open title: Subclassing of annotated types does not always work type: behavior versions: Python 3.10, Python 3.11, Python 3.9 _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue44969> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
