gh-104873: Add typing.get_protocol_members and typing.is_protocol (#104878)

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

Lib/typing.py

@@ -131,7 +131,9 @@ __all__ = [
     'get_args',
     'get_origin',
     'get_overloads',
+    'get_protocol_members',
     'get_type_hints',
+    'is_protocol',
     'is_typeddict',
     'LiteralString',
     'Never',
@@ -3337,3 +3339,43 @@ def override[F: _Func](method: F, /) -> F:
         # read-only property, TypeError if it's a builtin class.
         pass
     return method
+
+
+def is_protocol(tp: type, /) -> bool:
+    """Return True if the given type is a Protocol.
+
+    Example::
+
+        >>> from typing import Protocol, is_protocol
+        >>> class P(Protocol):
+        ...     def a(self) -> str: ...
+        ...     b: int
+        >>> is_protocol(P)
+        True
+        >>> is_protocol(int)
+        False
+    """
+    return (
+        isinstance(tp, type)
+        and getattr(tp, '_is_protocol', False)
+        and tp != Protocol
+    )
+
+
+def get_protocol_members(tp: type, /) -> frozenset[str]:
+    """Return the set of members defined in a Protocol.
+
+    Example::
+
+        >>> from typing import Protocol, get_protocol_members
+        >>> class P(Protocol):
+        ...     def a(self) -> str: ...
+        ...     b: int
+        >>> get_protocol_members(P)
+        frozenset({'a', 'b'})
+
+    Raise a TypeError for arguments that are not Protocols.
+    """
+    if not is_protocol(tp):
+        raise TypeError(f'{tp!r} is not a Protocol')
+    return frozenset(tp.__protocol_attrs__)