[3.10] bpo-44490: Add __parameters__ and __getitem__ to types.Union (GH-26980) (GH-27207)

Co-authored-by: Ken Jin <28750310+Fidget-Spinner@users.noreply.github.com>
Co-authored-by: Guido van Rossum <gvanrossum@gmail.com>.
(cherry picked from commit c45fa1a5d9b419cf13ad4b5a7cb453956495b83e)

Co-authored-by: Yurii Karabas <1998uriyyo@gmail.com>
Co-authored-by: Ken Jin <28750310+Fidget-Spinner@users.noreply.github.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/Lib/test/test_types.py b/Lib/test/test_types.py
index 0816f5a..2d0e33f 100644
--- a/Lib/test/test_types.py
+++ b/Lib/test/test_types.py
@@ -711,6 +711,8 @@ class TypesTests(unittest.TestCase):
         TV = typing.TypeVar('T')
         assert TV | str == typing.Union[TV, str]
         assert str | TV == typing.Union[str, TV]
+        self.assertIs((int | TV)[int], int)
+        self.assertIs((TV | int)[int], int)
 
     def test_union_args(self):
         def check(arg, expected):
@@ -742,6 +744,17 @@ class TypesTests(unittest.TestCase):
                 check(x | None, (x, type(None)))
                 check(None | x, (type(None), x))
 
+    def test_union_parameter_chaining(self):
+        T = typing.TypeVar("T")
+        S = typing.TypeVar("S")
+
+        self.assertEqual((float | list[T])[int], float | list[int])
+        self.assertEqual(list[int | list[T]].__parameters__, (T,))
+        self.assertEqual(list[int | list[T]][str], list[int | list[str]])
+        self.assertEqual((list[T] | list[S]).__parameters__, (T, S))
+        self.assertEqual((list[T] | list[S])[int, T], list[int] | list[T])
+        self.assertEqual((list[T] | list[S])[int, int], list[int])
+
     def test_or_type_operator_with_forward(self):
         T = typing.TypeVar('T')
         ForwardAfter = T | 'Forward'