Mypy type of concatenate tuples

This is was a known issue, but there appears to be no timeline for enabling mypywas fixed later in 2019 to do the correct type inference.

Concatenation of fixed-length tuples is not currently supported by mypy. As a workaround, you can construct a tuple from individual elements:

from typing import Tuple

def test(a: Tuple[str, str], b: Tuple[int, int]) -> Tuple[str, str, int, int]:
    return a[0], a[1], b[0], b[1]

or using unpacking if you have Python 3.5+:

def test(a: Tuple[str, str], b: Tuple[int, int]) -> Tuple[str, str, int, int]:
    return (*a, *b)  # the parentheses are required here

Here is a less-verbose workaround (python3.5+):

from typing import Tuple

def f(a: Tuple[str, str], b: Tuple[int, int]) -> Tuple[str, str, int, int]:
    return (*a, *b)