bpo-31333: Re-implement ABCMeta in C

Lib/abc.py

@@ -3,8 +3,6 @@
 
 """Abstract Base Classes (ABCs) according to PEP 3119."""
 
-from _weakrefset import WeakSet
-
 
 def abstractmethod(funcobj):
     """A decorator indicating abstract methods.
@@ -233,13 +231,6 @@ def __subclasscheck__(cls, subclass):
         return False
 
 
-class ABC(metaclass=ABCMeta):
-    """Helper class that provides a standard way to create an ABC using
-    inheritance.
-    """
-    __slots__ = ()
-
-
 def get_cache_token():
     """Returns the current ABC cache token.
 
@@ -248,3 +239,17 @@ def get_cache_token():
     with every call to ``register()`` on any ABC.
     """
     return ABCMeta._abc_invalidation_counter
+
+
+try:
+    from _abc import ABCMeta, get_cache_token
+except ImportError:
+    # We postpone this import to speed-up Python start-up time
+    from _weakrefset import WeakSet
+
+
+class ABC(metaclass=ABCMeta):
+    """Helper class that provides a standard way to create an ABC using
+    inheritance.
+    """
+    __slots__ = ()

Lib/test/libregrtest/refleak.py

@@ -113,7 +113,6 @@ def check_fd_deltas(deltas):
 def dash_R_cleanup(fs, ps, pic, zdc, abcs):
     import gc, copyreg
     import collections.abc
-    from weakref import WeakSet
 
     # Restore some original values.
     warnings.filters[:] = fs
@@ -137,7 +136,8 @@ def dash_R_cleanup(fs, ps, pic, zdc, abcs):
     abs_classes = filter(isabstract, abs_classes)
     for abc in abs_classes:
         for obj in abc.__subclasses__() + [abc]:
-            obj._abc_registry = abcs.get(obj, WeakSet()).copy()
+            for el in abcs.get(obj, set()):
+                obj._abc_registry.add(el)
             obj._abc_cache.clear()
             obj._abc_negative_cache.clear()
 

Modules/Setup.dist

@@ -118,6 +118,7 @@ _weakref _weakref.c		# weak references
 _functools _functoolsmodule.c   # Tools for working with functions and callable objects
 _operator _operator.c	        # operator.add() and similar goodies
 _collections _collectionsmodule.c # Container types
+_abc _abc.c                     # Abstract base classes
 itertools itertoolsmodule.c    # Functions creating iterators for efficient looping
 atexit atexitmodule.c      # Register functions to be run at interpreter-shutdown
 _signal signalmodule.c