bpo-44490: Improve typing module compatibility with types.Union (GH-27048)

1 files changed, 13 insertions, 5 deletions

diff --git a/Lib/typing.py b/Lib/typing.py
index 2f22868..f7386ea 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -196,7 +196,7 @@ def _type_repr(obj):
     return repr(obj)
 
 
-def _collect_type_vars(types, typevar_types=None):
+def _collect_type_vars(types_, typevar_types=None):
     """Collect all type variable contained
     in types in order of first appearance (lexicographic order). For example::
 
@@ -205,10 +205,10 @@ def _collect_type_vars(types, typevar_types=None):
     if typevar_types is None:
         typevar_types = TypeVar
     tvars = []
-    for t in types:
+    for t in types_:
         if isinstance(t, typevar_types) and t not in tvars:
             tvars.append(t)
-        if isinstance(t, (_GenericAlias, GenericAlias)):
+        if isinstance(t, (_GenericAlias, GenericAlias, types.Union)):
             tvars.extend([t for t in t.__parameters__ if t not in tvars])
     return tuple(tvars)
 
@@ -315,12 +315,14 @@ def _eval_type(t, globalns, localns, recursive_guard=frozenset()):
     """
     if isinstance(t, ForwardRef):
         return t._evaluate(globalns, localns, recursive_guard)
-    if isinstance(t, (_GenericAlias, GenericAlias)):
+    if isinstance(t, (_GenericAlias, GenericAlias, types.Union)):
         ev_args = tuple(_eval_type(a, globalns, localns, recursive_guard) for a in t.__args__)
         if ev_args == t.__args__:
             return t
         if isinstance(t, GenericAlias):
             return GenericAlias(t.__origin__, ev_args)
+        if isinstance(t, types.Union):
+            return functools.reduce(operator.or_, ev_args)
         else:
             return t.copy_with(ev_args)
     return t
@@ -1009,7 +1011,7 @@ class _GenericAlias(_BaseGenericAlias, _root=True):
         for arg in self.__args__:
             if isinstance(arg, self._typevar_types):
                 arg = subst[arg]
-            elif isinstance(arg, (_GenericAlias, GenericAlias)):
+            elif isinstance(arg, (_GenericAlias, GenericAlias, types.Union)):
                 subparams = arg.__parameters__
                 if subparams:
                     subargs = tuple(subst[x] for x in subparams)
@@ -1775,6 +1777,12 @@ def _strip_annotations(t):
         if stripped_args == t.__args__:
             return t
         return GenericAlias(t.__origin__, stripped_args)
+    if isinstance(t, types.Union):
+        stripped_args = tuple(_strip_annotations(a) for a in t.__args__)
+        if stripped_args == t.__args__:
+            return t
+        return functools.reduce(operator.or_, stripped_args)
+
     return t