review

python · JelleZijlstra · Apr 17, 2025 · Apr 16, 2025 · Apr 16, 2025 · Apr 16, 2025
commit f10143f5af96397f46ef0b19067208446fc3259b
@@ -3137,6 +3137,7 @@ def test_lazy_evaluation_with_subprotocols(self):
        class Base(Protocol):
            x: int

+        @runtime_checkable
        class Child(Base, Protocol):
            y: str


@@ -1925,9 +1925,11 @@ class _ProtocolMeta(ABCMeta):
    # This metaclass is somewhat unfortunate,
    # but is necessary for several reasons...
    def __new__(mcls, name, bases, namespace, /, **kwargs):
+        is_protocol = False
        if name == "Protocol" and bases == (Generic,):
            pass
        elif Protocol in bases:
+            is_protocol = True
            for base in bases:
                if not (
                    base in {object, Generic}
@@ -1942,7 +1944,8 @@ def __new__(mcls, name, bases, namespace, /, **kwargs):
                        f"got {base!r}"
                    )
        cls = super().__new__(mcls, name, bases, namespace, **kwargs)
-        cls.__protocol_attrs_cache__ = None
+        if is_protocol:
+            cls.__protocol_attrs_cache__ = None
        return cls

    def __subclasscheck__(cls, other):
@@ -2015,7 +2018,7 @@ def __protocol_attrs__(cls):
    def __non_callable_proto_members__(cls):
        # PEP 544 prohibits using issubclass()
        # with protocols that have non-method members.
-        non_callable_members = cls.__non_callable_proto_members_cache__
+        non_callable_members = cls.__non_callable_proto_members_cache__  # set by @runtime_checkable
        if non_callable_members is None:
            non_callable_members = set()
            for attr in cls.__protocol_attrs__:
-Original file line number
+Diff line change
@@ -3137,6 +3137,7 @@ def test_lazy_evaluation_with_subprotocols(self):
             class Base(Protocol):
                 x: int
+            @runtime_checkable
             class Child(Base, Protocol):
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                 y: str
-          Expand Down