From 93fcc04db7d047961c7d5f999d4d18911b6941d6 Mon Sep 17 00:00:00 2001
From: Ivan Levkivskyi <levkivskyi@gmail.com>
Date: Sat, 19 Nov 2016 13:20:47 +0100
Subject: [PATCH] Fix isinstance() for Protocols

---
 python2/test_typing.py | 8 +++++++-
 python2/typing.py      | 2 ++
 src/test_typing.py     | 7 +++++++
 src/typing.py          | 2 ++
 4 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/python2/test_typing.py b/python2/test_typing.py
index e95a10ffd..06791397b 100644
--- a/python2/test_typing.py
+++ b/python2/test_typing.py
@@ -480,7 +480,13 @@ def test_reversible(self):
     def test_protocol_instance_type_error(self):
         with self.assertRaises(TypeError):
             isinstance(0, typing.SupportsAbs)
-
+        class C1(typing.SupportsInt):
+            def __int__(self):
+                return 42
+        class C2(C1):
+            pass
+        c = C2()
+        self.assertIsInstance(c, C1)
 
 class GenericTests(BaseTestCase):
 
diff --git a/python2/typing.py b/python2/typing.py
index 993df27a8..eab198757 100644
--- a/python2/typing.py
+++ b/python2/typing.py
@@ -1462,6 +1462,8 @@ class _ProtocolMeta(GenericMeta):
     """
 
     def __instancecheck__(self, obj):
+        if _Protocol not in self.__bases__:
+            return super(_ProtocolMeta, self).__instancecheck__(obj)
         raise TypeError("Protocols cannot be used with isinstance().")
 
     def __subclasscheck__(self, cls):
diff --git a/src/test_typing.py b/src/test_typing.py
index 12bbf164a..183ede310 100644
--- a/src/test_typing.py
+++ b/src/test_typing.py
@@ -509,6 +509,13 @@ def test_reversible(self):
     def test_protocol_instance_type_error(self):
         with self.assertRaises(TypeError):
             isinstance(0, typing.SupportsAbs)
+        class C1(typing.SupportsInt):
+            def __int__(self) -> int:
+                return 42
+        class C2(C1):
+            pass
+        c = C2()
+        self.assertIsInstance(c, C1)
 
 
 class GenericTests(BaseTestCase):
diff --git a/src/typing.py b/src/typing.py
index fe22b2b5e..c7fe5ddb9 100644
--- a/src/typing.py
+++ b/src/typing.py
@@ -1503,6 +1503,8 @@ class _ProtocolMeta(GenericMeta):
     """
 
     def __instancecheck__(self, obj):
+        if _Protocol not in self.__bases__:
+            return super().__instancecheck__(obj)
         raise TypeError("Protocols cannot be used with isinstance().")
 
     def __subclasscheck__(self, cls):