Strict type checking like if type(x) is T: leads to wrong type restrictions

[Azureblade3808]

Environment data

• Language Server version: Pylance 2020.11.0
• OS and version: Window 7
• Python version (& distribution if applicable, e.g. Anaconda): Python 3.8.5

Actual Behavior

I have written a function to cast instances of any sub-classes of datetime.date as direct instances of datetime.date, so they can be used as SQL parameters.

import datetime as dt

def cast_as_builtin_date(date: dt.date) -> dt.date:
    if type(date) is dt.date:
        return date

    # Pylance says the type of `date` from now on will be 'Never',
    # but it still can necessarily be any sub-class of `datetime.date`
    # except for `datetime.date` itself.
    return dt.date(date.toordinal())

The type of argument date after the type check is determined as "Never" by Pylance, and as a result, the call of date.toordinal() is regarded problematic. It seems that Pylance treats if type(x) is T: just the same as if isinstance(x, T):, although they are different in some degrees.

Code Snippet / Additional Information

As a side note, code like if type(x) == T and if T is type(x) works just fine and can be used as a work-around.

[erictraut]

Thanks for the bug report. This will be fixed in the next release.

[jakebailey]

This issue has been fixed in version 2020.11.1, which we've just released. You can find the changelog here: https://github.com/microsoft/pylance-release/blob/master/CHANGELOG.md#2020111-11-november-2020