`datetime.datetime` should not inherit `datetime.date`

[tomasaschan]

datetime.datetime and datetime.date types cannot be used interchangeably, but the inheritance specified by the types in this project imply that they can. Consider the following code:

import datetime

def foo(d: datetime.date):
    return d < datetime.date.today()

foo(datetime.datetime.now()) # raises TypeError: can't compare datetime.datetime to datetime.date

Typechecking should indicate a problem - but it doesn't, resulting in a runtime exception instead.

I raised this issue with the Pyright project, but was redirected here.

[srittau]

datetime inherits from date at runtime. In my opinion that's a mistake, but in typeshed we follow the implementation. Not inheriting in typeshed causes other problems.

[srittau]

Previous discussions in #3805 and python/mypy#9015.

[tomasaschan]

Thanks for linking me to those discussions! I'm glad that at least python/mypy#9015 is not closed yet, even if it also is not seeing much activity...