Cleaner solution

python · JelleZijlstra · Jun 5, 2023 · Jun 2, 2023 · Jun 2, 2023 · Jun 2, 2023
commit b85a3205c4b22942c9cb4ce0f8619d7b04d2ffe0
@@ -1805,6 +1805,8 @@ def __subclasscheck__(cls, other):
     def __instancecheck__(cls, instance):
         # We need this method for situations where attributes are
         # assigned in __init__.
+        if cls is Protocol:
+            return type.__instancecheck__(cls, instance)
         if not getattr(cls, "_is_protocol", False):
             # i.e., it's a concrete subclass of a protocol
             return super().__instancecheck__(instance)
@@ -1864,7 +1866,7 @@ def meth(self) -> T:
                 ...
     """
     __slots__ = ()
-    _is_protocol = False
+    _is_protocol = True
     _is_runtime_protocol = False
 
     def __init_subclass__(cls, *args, **kwargs):
@@ -1906,7 +1908,7 @@ def _proto_hook(other):
 
         # ... otherwise check consistency of bases, and prohibit instantiation.
         for base in cls.__bases__:
-            if not (base in {object, Generic, Protocol} or
+            if not (base in (object, Generic) or
                     base.__module__ in _PROTO_ALLOWLIST and
                     base.__name__ in _PROTO_ALLOWLIST[base.__module__] or
                     issubclass(base, Generic) and getattr(base, '_is_protocol', False)):