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assigning a Tuple[int, ...] to an Iterable[int] results in builtins.None or <nothing> #4466
Description
Bug with this code:
from typing import Iterable, Tuple
x: Iterable[int] = ()
y: Tuple[int, ...] = (1, 2, 3)
x = y
reveal_type(x)
Actual result (on mypy master, Python 3.6):
tuplebug.py:9: error: Revealed type is 'builtins.None'
Actual result with --strict-optional:
tuplebug.py:9: error: Revealed type is '<nothing>'
Expected result:
The revealed type should be Tuple[int, ...].
Via git bisect, I find that this bug was introduced recently, in #4238 (cc @elazarg, @JukkaL ).
Activity
carljm commentedon Jan 13, 2018
(We saw this as a regression false positive on real code, when upgrading mypy.)
gvanrossum commentedon Jan 13, 2018
Ideally we should fix this before the next mypy release (which hasn't been scheduled yet).
elazarg commentedon Jan 14, 2018
Thanks for the report.
I'd note that the following also fails, and is important to test since
Tuple[int, ...]andTuple[int, int]are handled quite differently inside mypy:The issue seems to be subtle.
emmatyping commentedon Jul 2, 2018
@ilevkivskyi I think this is the same issue I saw in #5303. I am raising priority to high, since this was a regression and came up again (and I expect it is not an uncommon pattern).
Improve Tuple/Sequence/Iterable overlapping (#5315)