python · miss-islington · Apr 7, 2023 · Apr 7, 2023
@@ -2572,6 +2572,22 @@ def meth(x): ...
        class PG(Protocol[T]):
            def meth(x): ...

+        @runtime_checkable
+        class WeirdProto(Protocol):
+            meth = str.maketrans
+
+        @runtime_checkable
+        class WeirdProto2(Protocol):
+            meth = lambda *args, **kwargs: None
+
+        class CustomCallable:
+            def __call__(self, *args, **kwargs):
+                pass
+
+        @runtime_checkable
+        class WeirderProto(Protocol):
+            meth = CustomCallable()
+
        class BadP(Protocol):
            def meth(x): ...

@@ -2581,8 +2597,15 @@ def meth(x): ...
        class C:
            def meth(x): ...

-        self.assertIsInstance(C(), P)
-        self.assertIsInstance(C(), PG)
+        class C2:
+            def __init__(self):
+                self.meth = lambda: None
+
+        for klass in C, C2:
+            for proto in P, PG, WeirdProto, WeirdProto2, WeirderProto:
+                with self.subTest(klass=klass.__name__, proto=proto.__name__):
+                    self.assertIsInstance(klass(), proto)
+
        with self.assertRaises(TypeError):
            isinstance(C(), PG[T])
        with self.assertRaises(TypeError):
@@ -2735,6 +2758,20 @@ def __init__(self, x):
        self.assertIsInstance(C(1), P)
        self.assertIsInstance(C(1), PG)

+    def test_protocols_isinstance_monkeypatching(self):
+        @runtime_checkable
+        class HasX(Protocol):
+            x: int
+
+        class Foo: ...
+
+        f = Foo()
+        self.assertNotIsInstance(f, HasX)
+        f.x = 42
+        self.assertIsInstance(f, HasX)
+        del f.x
+        self.assertNotIsInstance(f, HasX)
+
    def test_protocol_checks_after_subscript(self):
        class P(Protocol[T]): pass
        class C(P[T]): pass