Backport performance improvements to runtime-checkable protocols

CHANGELOG.md

@@ -7,6 +7,18 @@
   (originally by Yurii Karabas), ensuring that `isinstance()` calls on
   protocols raise `TypeError` when the protocol is not decorated with
   `@runtime_checkable`. Patch by Alex Waygood.
+- Backport several significant performance improvements to runtime-checkable
+  protocols that have been made in Python 3.12 (see
+  https://github.com/python/cpython/issues/74690 for details). Patch by Alex
+  Waygood.
+
+  A side effect of one of the performance improvements is that the members of
+  a runtime-checkable protocol are now considered “frozen” at runtime as soon
+  as the class has been created. Monkey-patching attributes onto a
+  runtime-checkable protocol will still work, but will have no impact on
+  `isinstance()` checks comparing objects to the protocol. See
+  ["What's New in Python 3.12"](https://docs.python.org/3.12/whatsnew/3.12.html#typing)
+  for more details.
 
 # Release 4.5.0 (February 14, 2023)
 

src/test_typing_extensions.py

@@ -3452,9 +3452,11 @@ def test_typing_extensions_defers_when_possible(self):
             'is_typeddict',
         }
         if sys.version_info < (3, 10):
-            exclude |= {'get_args', 'get_origin', 'Protocol', 'runtime_checkable'}
+            exclude |= {'get_args', 'get_origin'}
         if sys.version_info < (3, 11):
             exclude |= {'final', 'NamedTuple', 'Any'}
+        if sys.version_info < (3, 12):
+            exclude |= {'Protocol', 'runtime_checkable'}
         for item in typing_extensions.__all__:
             if item not in exclude and hasattr(typing, item):
                 self.assertIs(

src/typing_extensions.py

@@ -403,6 +403,7 @@ def clear_overloads():
     "_is_runtime_protocol", "__dict__", "__slots__", "__parameters__",
     "__orig_bases__", "__module__", "_MutableMapping__marker", "__doc__",
     "__subclasshook__", "__orig_class__", "__init__", "__new__",
+    "__protocol_attrs__", "__callable_proto_members_only__",
 }
 
 if sys.version_info < (3, 8):
@@ -420,19 +421,15 @@ def clear_overloads():
 def _get_protocol_attrs(cls):
     attrs = set()
     for base in cls.__mro__[:-1]:  # without object
-        if base.__name__ in ('Protocol', 'Generic'):
+        if base.__name__ in {'Protocol', 'Generic'}:
             continue
         annotations = getattr(base, '__annotations__', {})
-        for attr in list(base.__dict__.keys()) + list(annotations.keys()):
+        for attr in (*base.__dict__, *annotations):
             if (not attr.startswith('_abc_') and attr not in _EXCLUDED_ATTRS):
                 attrs.add(attr)
     return attrs
 
 
-def _is_callable_members_only(cls):
-    return all(callable(getattr(cls, attr, None)) for attr in _get_protocol_attrs(cls))
-
-
 def _maybe_adjust_parameters(cls):
     """Helper function used in Protocol.__init_subclass__ and _TypedDictMeta.__new__.
 
@@ -442,7 +439,7 @@ def _maybe_adjust_parameters(cls):
     """
     tvars = []
     if '__orig_bases__' in cls.__dict__:
-        tvars = typing._collect_type_vars(cls.__orig_bases__)
+        tvars = _collect_type_vars(cls.__orig_bases__)
         # Look for Generic[T1, ..., Tn] or Protocol[T1, ..., Tn].
         # If found, tvars must be a subset of it.
         # If not found, tvars is it.
@@ -480,9 +477,9 @@ def _caller(depth=2):
         return None
 
 
-# A bug in runtime-checkable protocols was fixed in 3.10+,
-# but we backport it to all versions
-if sys.version_info >= (3, 10):
+# The performance of runtime-checkable protocols is significantly improved on Python 3.12,
+# so we backport the 3.12 version of Protocol to Python <=3.11
+if sys.version_info >= (3, 12):
     Protocol = typing.Protocol
     runtime_checkable = typing.runtime_checkable
 else:
@@ -500,6 +497,15 @@ def _no_init(self, *args, **kwargs):
     class _ProtocolMeta(abc.ABCMeta):
         # This metaclass is a bit unfortunate and exists only because of the lack
         # of __instancehook__.
+        def __init__(cls, *args, **kwargs):
+            super().__init__(*args, **kwargs)
+            cls.__protocol_attrs__ = _get_protocol_attrs(cls)
+            # PEP 544 prohibits using issubclass()
+            # with protocols that have non-method members.
+            cls.__callable_proto_members_only__ = all(
+                callable(getattr(cls, attr, None)) for attr in cls.__protocol_attrs__
+            )
+
         def __instancecheck__(cls, instance):
             # We need this method for situations where attributes are
             # assigned in __init__.
@@ -511,17 +517,22 @@ def __instancecheck__(cls, instance):
             ):
                 raise TypeError("Instance and class checks can only be used with"
                                 " @runtime_checkable protocols")
-            if ((not is_protocol_cls or
-                 _is_callable_members_only(cls)) and
-                    issubclass(instance.__class__, cls)):
+
+            if super().__instancecheck__(instance):
                 return True
+
             if is_protocol_cls:
-                if all(hasattr(instance, attr) and
-                       (not callable(getattr(cls, attr, None)) or
-                        getattr(instance, attr) is not None)
-                       for attr in _get_protocol_attrs(cls)):
+                for attr in cls.__protocol_attrs__:
+                    try:
+                        val = getattr(instance, attr)
+                    except AttributeError:
+                        break
+                    if val is None and callable(getattr(cls, attr, None)):
+                        break
+                else:
                     return True
-            return super().__instancecheck__(instance)
+
+            return False
 
     class Protocol(metaclass=_ProtocolMeta):
         # There is quite a lot of overlapping code with typing.Generic.
@@ -613,15 +624,15 @@ def _proto_hook(other):
                         return NotImplemented
                     raise TypeError("Instance and class checks can only be used with"
                                     " @runtime protocols")
-                if not _is_callable_members_only(cls):
+                if not cls.__callable_proto_members_only__:
                     if _allow_reckless_class_checks():
                         return NotImplemented
                     raise TypeError("Protocols with non-method members"
                                     " don't support issubclass()")
                 if not isinstance(other, type):
                     # Same error as for issubclass(1, int)
                     raise TypeError('issubclass() arg 1 must be a class')
-                for attr in _get_protocol_attrs(cls):
+                for attr in cls.__protocol_attrs__:
                     for base in other.__mro__:
                         if attr in base.__dict__:
                             if base.__dict__[attr] is None:
@@ -1819,6 +1830,10 @@ class Movie(TypedDict):
 
 if hasattr(typing, "Unpack"):  # 3.11+
     Unpack = typing.Unpack
+
+    def _is_unpack(obj):
+        return get_origin(obj) is Unpack
+
 elif sys.version_info[:2] >= (3, 9):
     class _UnpackSpecialForm(typing._SpecialForm, _root=True):
         def __repr__(self):