gh-74690: typing: Don't unnecessarily call _get_protocol_attrs twice in _ProtocolMeta.__instancecheck__

Lib/typing.py

@@ -1931,9 +1931,9 @@ def _get_protocol_attrs(cls):
  return attrs
 
 
-def _is_callable_members_only(cls):
+def _is_callable_members_only(cls, protocol_attrs):
  # PEP 544 prohibits using issubclass() with protocols that have non-method members.
- return all(callable(getattr(cls, attr, None)) for attr in _get_protocol_attrs(cls))
+ return all(callable(getattr(cls, attr, None)) for attr in protocol_attrs)
 
 
 def _no_init_or_replace_init(self, *args, **kwargs):
@@ -2000,24 +2000,32 @@ class _ProtocolMeta(ABCMeta):
  def __instancecheck__(cls, instance):
  # We need this method for situations where attributes are
  # assigned in __init__.
+ is_protocol_cls = getattr(cls, "_is_protocol", False)
  if (
-getattr(cls, '_is_protocol', False) and
+is_protocol_cls and
  not getattr(cls, '_is_runtime_protocol', False) and
  not _allow_reckless_class_checks(depth=2)
  ):
  raise TypeError("Instance and class checks can only be used with"
  " @runtime_checkable protocols")
 
- if ((not getattr(cls, '_is_protocol', False) or
- _is_callable_members_only(cls)) and
- issubclass(instance.__class__, cls)):
+ if not is_protocol_cls and issubclass(instance.__class__, cls):
  return True
- if cls._is_protocol:
+
+ protocol_attrs = _get_protocol_attrs(cls)
+
+ if (
+ _is_callable_members_only(cls, protocol_attrs)
+ and issubclass(instance.__class__, cls)
+ ):
+ return True
+
+ if is_protocol_cls:
  if all(hasattr(instance, attr) and
  # All *methods* can be blocked by setting them to None.
  (not callable(getattr(cls, attr, None)) or
  getattr(instance, attr) is not None)
- for attr in _get_protocol_attrs(cls)):
+ for attr in protocol_attrs):
  return True
  return super().__instancecheck__(instance)
 
@@ -2074,7 +2082,10 @@ def _proto_hook(other):
  return NotImplemented
  raise TypeError("Instance and class checks can only be used with"
  " @runtime_checkable protocols")
- if not _is_callable_members_only(cls):
+
+ protocol_attrs = _get_protocol_attrs(cls)
+
+ if not _is_callable_members_only(cls, protocol_attrs):
  if _allow_reckless_class_checks():
  return NotImplemented
  raise TypeError("Protocols with non-method members"
@@ -2084,7 +2095,7 @@ def _proto_hook(other):
  raise TypeError('issubclass() arg 1 must be a class')
 
  # Second, perform the actual structural compatibility check.
- for attr in _get_protocol_attrs(cls):
+ for attr in protocol_attrs:
  for base in other.__mro__:
  # Check if the members appears in the class dictionary...
  if attr in base.__dict__: