Union type hint with Python 3.6.0 is no longer a class

[gaborbernat]

Here's an interesting interaction, with Python 3.6 the union type hint is no longer a class (while tuple still is),, as opposed to 3.5 where both are. Is this a bug, or a valid change? And if valid what's the reason for the inconsistency?

# coding=utf-8
""" Test type hints. """
import inspect
from typing import Tuple, Union, get_type_hints


def tuple_test(param: Tuple[str, ...]):
    """

    :param param:
    :return:
    """
    return param


def union_test(param: Union[str, int]):
    """

    :param param:
    :return:
    """
    return param

print(inspect.isclass(get_type_hints(tuple_test)['param']))
print(inspect.isclass(get_type_hints(union_test)['param']))

Produces the following output:

bernat@uvm ~/work/git/sphinx-autodoc-typehints (master●)$ python --version
Python 3.5.0
bernat@uvm ~/work/git/sphinx-autodoc-typehints (master●)$ python tests/docs/annotation/test_code/__init__.py
True
True
bernat@uvm ~/work/git/sphinx-autodoc-typehints (master●)$ pyenv local 3.6.0
bernat@uvm ~/work/git/sphinx-autodoc-typehints (master●)$ python --version
Python 3.6.0
bernat@uvm ~/work/git/sphinx-autodoc-typehints (master●)$ python tests/docs/annotation/test_code/__init__.py
True
False

[ilevkivskyi]

This is intentional. Union has no way to be a valid runtime class (one can neither inherit it, nor instantiate). At the same time Tuple has a runtime counterpart tuple equivalent to Tuple[Any, ...].

By subclassing Tuple one can indicate that a certain class supports "tuple protocol" and there is no way to annotate __getitem__ as expressive as inheriting from Tuple[str, int].