Fix #27014 -- infinite recursion using typing.py.

1 files changed, 22 insertions, 3 deletions

diff --git a/Lib/test/test_typing.py b/Lib/test/test_typing.py
index 90bad77..f9e54b2 100644
--- a/Lib/test/test_typing.py
+++ b/Lib/test/test_typing.py
@@ -1,4 +1,5 @@
 import contextlib
+import collections
 import pickle
 import re
 import sys
@@ -1218,13 +1219,17 @@ class CollectionsAbcTests(BaseTestCase):
         with self.assertRaises(TypeError):
             typing.List[int]()
 
-    def test_list_subclass_instantiation(self):
+    def test_list_subclass(self):
 
         class MyList(typing.List[int]):
             pass
 
         a = MyList()
         self.assertIsInstance(a, MyList)
+        self.assertIsInstance(a, typing.Sequence)
+
+        self.assertIsSubclass(MyList, list)
+        self.assertNotIsSubclass(list, MyList)
 
     def test_no_dict_instantiation(self):
         with self.assertRaises(TypeError):
@@ -1234,13 +1239,17 @@ class CollectionsAbcTests(BaseTestCase):
         with self.assertRaises(TypeError):
             typing.Dict[str, int]()
 
-    def test_dict_subclass_instantiation(self):
+    def test_dict_subclass(self):
 
         class MyDict(typing.Dict[str, int]):
             pass
 
         d = MyDict()
         self.assertIsInstance(d, MyDict)
+        self.assertIsInstance(d, typing.MutableMapping)
+
+        self.assertIsSubclass(MyDict, dict)
+        self.assertNotIsSubclass(dict, MyDict)
 
     def test_no_defaultdict_instantiation(self):
         with self.assertRaises(TypeError):
@@ -1250,7 +1259,7 @@ class CollectionsAbcTests(BaseTestCase):
         with self.assertRaises(TypeError):
             typing.DefaultDict[str, int]()
 
-    def test_defaultdict_subclass_instantiation(self):
+    def test_defaultdict_subclass(self):
 
         class MyDefDict(typing.DefaultDict[str, int]):
             pass
@@ -1258,6 +1267,9 @@ class CollectionsAbcTests(BaseTestCase):
         dd = MyDefDict()
         self.assertIsInstance(dd, MyDefDict)
 
+        self.assertIsSubclass(MyDefDict, collections.defaultdict)
+        self.assertNotIsSubclass(collections.defaultdict, MyDefDict)
+
     def test_no_set_instantiation(self):
         with self.assertRaises(TypeError):
             typing.Set()
@@ -1338,6 +1350,13 @@ class CollectionsAbcTests(BaseTestCase):
         self.assertEqual(len(MMB[str, str]()), 0)
         self.assertEqual(len(MMB[KT, VT]()), 0)
 
+        self.assertNotIsSubclass(dict, MMA)
+        self.assertNotIsSubclass(dict, MMB)
+
+        self.assertIsSubclass(MMA, typing.Mapping)
+        self.assertIsSubclass(MMB, typing.Mapping)
+        self.assertIsSubclass(MMC, typing.Mapping)
+
 
 class OtherABCTests(BaseTestCase):