datetime inherits from date

You may be surprised to know that datetime is a subclass of date. This doesn’t seem problematic at first, but it leads to odd behavior. Most notably, the fact that date and datetime cannot be compared violates basic assumptions of how subclasses should work. The datetime/date inheritance is now widely considered to be a design flaw in the standard library.

# Breaks on a datetime, even though it's a subclass
def is_future(d: date) -> bool:
    return d > date.today()

# Some methods inherited from `date` don't make sense
datetime.today()  # fun exercise: what does this return?

How whenever solves this

Whenever separates the concepts of date and datetime completely. There is no inheritance relationship between Date and PlainDateTime/ZonedDateTime. This means you can catch mistakes at compile time, and all comparisons behave intuitively:

>>> from whenever import Date, PlainDateTime
>>> d = Date(2024, 7, 4)
>>> dt = PlainDateTime(2024, 7, 4, 12, 0, 0)
>>> d > dt  # type checker will catch this