How should typing_extensions TypeVar default be used with a Generic?

[gandhis1]

Example (link to Mypy playground):

from typing_extensions import Generic, TypeVar

T = TypeVar("T", default=int)

class ListWrapper(Generic[T]):
    def __init__(self, input_list: list[T]) -> None:
        self.input_list = input_list


def print_wrapper(wrapper_instance: ListWrapper) -> None:  # main.py:10: error: Missing type parameters for generic type "ListWrapper"  [type-arg]
    print(wrapper_instance.input_list)

x = ListWrapper([1, 2, 3])
reveal_type(x)  # main.py:14: note: Revealed type is "__main__.ListWrapper[builtins.int]"
print_wrapper(x)

I suspect I am just misunderstanding the way this works. I had the expectation that I would no longer need to specialize ListWrapper, and the omission of the TypeVar would be assumed to mean ListWrapper[int]. Could someone please clarify?

[Gobot1234]

This is a bug in mypy's implementation (pyright's works fine here https://pyright-play.net/?code=GYJw9gtgBALgngBwJYDsDmB9ApgDxllAZyTCKiQgTBBigHECsQkBjAGigBVEsA1AQxABYAFCjOUALxceAkAAoARJ0UcAJlmD8ArgBsYk1DACUo0S139ChKABkkhGAHUQ-BAibyGKJqwDanAC6xgBcolARUBrAUBgYqEgwcfKEWLrAHKgI2km6DjAhUHmOAcFQALQAfFAAcqRYYSKRzVCp6QB0WTkYxbTSXbn5ZmIi0VAIzChJAO6u7p6zbh4g8UQw-CgsDXb5LktMxhXVdT6FUADEUBD8qO0IcCEAjAAMhUzgIIUAsg7E6LA8caCfgQLD4EA2YDUKBoRjMFgAjxQRT2Rx7eYgRQRPzwDzlQRoQLhSITIzyRYY1aODZbToobKDRymEY4KQ7NFzZbyPyPDgAJg4AGZgqIQFgAG5Yfi6DC4rDyHCHC5XG4oO4PR4AFkKKDA+EKACUJVLdFg1IisOQbIo4tdUHF2qjnJymH4AEbaJD6VCEOkwQKKUSkqYYClcxVAA). It should work according to the PEP.

[erictraut]

I don't think it's fair to call this a "bug" in mypy. Mypy simply hasn't implemented support for PEP 696. This is understandable given that PEP 696 is still in draft form and hasn't been accepted by the steering council.

Pyright does have (provisional) support for the latest draft of PEP 696 if you want to play with it.

[gandhis1]

Thank you. Linking to the corresponding issue on Mypy's issue tracker for others' reference:

python/mypy#14851