Make weak references subclassable:

- weakref.ref and weakref.ReferenceType will become aliases for each
  other

- weakref.ref will be a modern, new-style class with proper __new__
  and __init__ methods

- weakref.WeakValueDictionary will have a lighter memory footprint,
  using a new weakref.ref subclass to associate the key with the
  value, allowing us to have only a single object of overhead for each
  dictionary entry (currently, there are 3 objects of overhead per
  entry: a weakref to the value, a weakref to the dictionary, and a
  function object used as a weakref callback; the weakref to the
  dictionary could be avoided without this change)

- a new macro, PyWeakref_CheckRefExact(), will be added

- PyWeakref_CheckRef() will check for subclasses of weakref.ref

This closes SF patch #983019.

1 files changed, 6 insertions, 1 deletions

diff --git a/Include/weakrefobject.h b/Include/weakrefobject.h
index effa0ed..3503892 100644
--- a/Include/weakrefobject.h
+++ b/Include/weakrefobject.h
@@ -22,11 +22,16 @@ PyAPI_DATA(PyTypeObject) _PyWeakref_RefType;
 PyAPI_DATA(PyTypeObject) _PyWeakref_ProxyType;
 PyAPI_DATA(PyTypeObject) _PyWeakref_CallableProxyType;
 
-#define PyWeakref_CheckRef(op) \
+#define PyWeakref_CheckRef(op) PyObject_TypeCheck(op, &_PyWeakref_RefType)
+#define PyWeakref_CheckRefExact(op) \
         ((op)->ob_type == &_PyWeakref_RefType)
 #define PyWeakref_CheckProxy(op) \
         (((op)->ob_type == &_PyWeakref_ProxyType) || \
          ((op)->ob_type == &_PyWeakref_CallableProxyType))
+
+/* This macro calls PyWeakref_CheckRef() last since that can involve a
+   function call; this makes it more likely that the function call
+   will be avoided. */
 #define PyWeakref_Check(op) \
         (PyWeakref_CheckRef(op) || PyWeakref_CheckProxy(op))