Fix #16832 - expose cache validity checking support in ABCMeta
diff --git a/Lib/abc.py b/Lib/abc.py
index e807895..264c60c 100644
--- a/Lib/abc.py
+++ b/Lib/abc.py
@@ -5,6 +5,7 @@
from _weakrefset import WeakSet
+
def abstractmethod(funcobj):
"""A decorator indicating abstract methods.
@@ -124,6 +125,8 @@
# A global counter that is incremented each time a class is
# registered as a virtual subclass of anything. It forces the
# negative cache to be cleared before its next use.
+ # Note: this counter is private. Use `abc.get_cache_token()` for
+ # external code.
_abc_invalidation_counter = 0
def __new__(mcls, name, bases, namespace):
@@ -227,8 +230,19 @@
cls._abc_negative_cache.add(subclass)
return False
+
class ABC(metaclass=ABCMeta):
"""Helper class that provides a standard way to create an ABC using
inheritance.
"""
pass
+
+
+def get_cache_token():
+ """Returns the current ABC cache token.
+
+ The token is an opaque integer identifying the current version of
+ the ABC cache for virtual subclasses. This number changes with
+ every call to ``register()`` on any ABC.
+ """
+ return ABCMeta._abc_invalidation_counter