How to specify multiple paramater Union types as type hints in Python 3.9

Question

For example, if my code were to be like this in Python 3.10 :

from typing import Union

class TupleInvalid(Exception):
    pass

TestValue = Union[int, str, float]
TestListA = tuple[str, TestValue]
TestListB = tuple[str, TestValue, TestValue]

def two_or_three(*tuples: TestListA | TestListB) -> str:

    for x in tuples:
        if isinstance(x[0], str):
            if len(x) == 2:
                return 'two'
            elif len(x) == 3:
                return 'three'
            else:
                raise TupleInvalid('Tuple should be 2 or 3 long')
        else:
            raise TupleInvalid(
                'Tuple should be (<str>, <int | float | str>, \
                <int | float | str> (optional)')


print(two_or_three(("test", 3, 4.5)))
print(two_or_three(("testing", 'hi')))

My linter would be able to pick up on the fact the argument *tuples should be a tuple consisting of either tuple[str, TestValue] or tuple[str, TestValue, TestValue] . In Python 3.9 however, it doesn't seem to be able to work. I tried making it an Union[TestListA, TestListB] but that just gives a lot of errors. ( TypeError: Cannot instantiate typing.Union)

Using or does not give any errors but my linter doesn't seem to be able to find the possible second type then.

(*tuples: TestListA or TestListB)

Answer 1

Python 3.9 doesn't have that feature. It is introduced in Python 3.10.