bpo-32346: speed up slot lookup during class creation

Instead of looking up every possible slot in every class along the MRO (generating possibly hundreds of dict lookups), cache the known descriptors of each type so that finding them again is simply a matter of walking a tuple.
python · pitrou · Dec 15, 2017 · Dec 19, 2017 · Dec 19, 2017 · Dec 19, 2017
commit 4b2e41c14789378ca2c02a46d579641dd8423a37
diff --git a/Include/object.h b/Include/object.h
@@ -424,6 +424,8 @@ typedef struct _typeobject {
 
     destructor tp_finalize;
 
+    PyObject *tp_defined_slots;
+
 #ifdef COUNT_ALLOCS
     /* these must be last and never explicitly initialized */
     Py_ssize_t tp_allocs;
@@ -656,17 +658,21 @@ given type object has a specified feature.
 #define Py_TPFLAGS_BASE_EXC_SUBCLASS    (1UL << 30)
 #define Py_TPFLAGS_TYPE_SUBCLASS        (1UL << 31)
 
-#define Py_TPFLAGS_DEFAULT  ( \
-                 Py_TPFLAGS_HAVE_STACKLESS_EXTENSION | \
-                 Py_TPFLAGS_HAVE_VERSION_TAG | \
-                0)
-
 /* NOTE: The following flags reuse lower bits (removed as part of the
  * Python 3.0 transition). */
 
 /* Type structure has tp_finalize member (3.4) */
 #define Py_TPFLAGS_HAVE_FINALIZE (1UL << 0)
 
+/* Type structure has tp_defined_slots member (3.7) */
+#define Py_TPFLAGS_HAVE_DEFINED_SLOTS (1UL << 1)
+
+#define Py_TPFLAGS_DEFAULT  ( \
+                 Py_TPFLAGS_HAVE_STACKLESS_EXTENSION | \
+                 Py_TPFLAGS_HAVE_VERSION_TAG | \
+                 Py_TPFLAGS_HAVE_DEFINED_SLOTS | \
+                0)
+
 #ifdef Py_LIMITED_API
 #define PyType_HasFeature(t,f)  ((PyType_GetFlags(t) & (f)) != 0)
 #else

diff --git a/Lib/test/test_sys.py b/Lib/test/test_sys.py
@@ -1113,7 +1113,7 @@ def delx(self): del self.__x
         check((1,2,3), vsize('') + 3*self.P)
         # type
         # static type: PyTypeObject
-        fmt = 'P2n15Pl4Pn9Pn11PIP'
+        fmt = 'P2n15Pl4Pn9Pn11PI2P'
         if hasattr(sys, 'getcounts'):
             fmt += '3n2P'
         s = vsize(fmt)