bpo-43772: Fix TypeVar.__ror__ (GH-25339)

Author: JelleZijlstra

Lib/test/test_typing.py

@@ -186,6 +186,16 @@ def test_union_unique(self):
  self.assertEqual(Union[X, int].__parameters__, (X,))
  self.assertIs(Union[X, int].__origin__, Union)
 
+ def test_or(self):
+ X = TypeVar('X')
+ # use a string because str doesn't implement
+ # __or__/__ror__ itself
+ self.assertEqual(X | "x", Union[X, "x"])
+ self.assertEqual("x" | X, Union["x", X])
+ # make sure the order is correct
+ self.assertEqual(get_args(X | "x"), (X, ForwardRef("x")))
+ self.assertEqual(get_args("x" | X), (ForwardRef("x"), X))
+
  def test_union_constrained(self):
  A = TypeVar('A', str, bytes)
  self.assertNotEqual(Union[A, str], Union[A])

Lib/typing.py

@@ -648,8 +648,8 @@ def __init__(self, bound, covariant, contravariant):
  def __or__(self, right):
  return Union[self, right]
 
- def __ror__(self, right):
- return Union[self, right]
+ def __ror__(self, left):
+ return Union[left, self]
 
  def __repr__(self):
  if self.__covariant__:

Misc/NEWS.d/next/Library/2021-04-10-19-14-49.bpo-43772.Bxq0zQ.rst

@@ -0,0 +1 @@
+Fixed the return value of ``TypeVar.__ror__``. Patch by Jelle Zijlstra.