datetime.datetime.__init__ stub bug?

[smontanaro]

Stumbled on this today (Python 2 or Python 3):

print(datetime.datetime(2017, 1, 1, 12, 12, 12))
fields = [2017, 1, 1, 12, 12, 12]
print(datetime.datetime(*fields))

When run, both prints produce the expected output, but mypy complains about the second construction:

Argument 1 to "datetime" has incompatible type *List[int]; expected "tzinfo"

I'm using mypy 0.4.6 and a set of typeshed definitions I installed locally on Dec 6. Sorry I can't be more specific than that. Getting stuff into my work environment is tedious. If you can't reproduce this with the latest mypy+typeshed, just close it.

The stub for datetime.datetime.__init__ in what I have looks broken to me though. For both stdlib/2 and stdlib/3 it suggests that only the type of the year is known to be an int. Everything else other than tzinfo is given as "...". In fact, in Python 3, at least, everything after the day should be optional. Year, month, and day must be ints.

[gvanrossum]

Argument 1 to "datetime" has incompatible type *List[int]; expected "tzinfo"

That's because of mypy's limited understanding of *args -- it doesn't keep track of the length of the list of fields so it tries to match the item type (int) with all the arguments. It'll work if you use a tuple instead.

Everything else other than tzinfo is given as "...".

Oh, but they are optional. The ... is a non-specific default value. So e.g.

def foo(a: int, b: int = ...): ...

just means that foo() has one mandatory arg and one optional arg. So I believe the stub is correct.

[JelleZijlstra]

As Guido explained, there isn't a typeshed bug here, so I'm closing this issue. However, I think the error @smontanaro got indicates a mypy bug, which I reported at python/mypy#3224.