mypy does not recognize conversion between fixed length list and tuple

• Are you reporting a bug, or opening a feature request?

I believe this is a bug

• Please insert below the code you are checking with mypy,
  or a mock-up repro if the source is private. We would appreciate
  if you try to simplify your case to a minimal repro.

Minimal example to reproduce:

from typing import List, Tuple


def get_point_as_list() -> List[int]:
    return [1, 2]


def point_to_tuple(pt: List[int]) -> Tuple[int, int]:
    assert len(pt) == 2
    return tuple(pt)


if __name__ == "__main__":
    l = get_point_as_list()
    p = point_to_tuple(l)
    print(repr(p))

• What is the actual behavior/output?

mypy test.py

test.py:10: error: Incompatible return value type (got "Tuple[int, ...]", expected "Tuple[int, int]")

• What is the behavior/output you expect?

mypy should evaluate this as correct code

• What are the versions of mypy and Python you are using?
  Do you see the same issue after installing mypy from Git master?

$ mypy --version
mypy 0.720

$ python --version
Python 3.7.3

Inizia eseguendo con mypy l'esempio segnalato in test.py e conferma la diagnostica di incompatibilità tra Tuple[int, ...] e Tuple[int, int]. Traccia il modo in cui il type checker gestisce la conversione tramite tuple() di una lista di lunghezza fissa e verifica che l'esempio venga accettato senza indebolire controlli di tipo non correlati.