From: Raymond Hettinger <python@rcn.com>
Date: Thu, 29 Jul 2004 23:31:29 +0000 (+0000)
Subject: * Simplify and speed-up list_resize().  Relying on the newly documented
X-Git-Tag: v2.4a2~103
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=c0aaa2db4f7c33c490f91d00c894ffa6395c74fc;p=python

* Simplify and speed-up list_resize().  Relying on the newly documented
  invariants allows the ob_item != NULL check to be replaced with an
  assertion.

* Added assertions to list_init() which document and verify that the
  tp_new slot establishes the invariants.  This may preclude a future
  bug if a custom tp_new slot is written.
---

diff --git a/Objects/listobject.c b/Objects/listobject.c
index 452ffe5a5c..61edd45f3b 100644
--- a/Objects/listobject.c
+++ b/Objects/listobject.c
@@ -19,9 +19,8 @@ list_resize(PyListObject *self, int newsize)
 	   current size, then proceed with the realloc() to shrink the list.
 	*/
 
-	if (self->allocated >= newsize &&
-	    self->ob_size < newsize + 16 &&
-	    self->ob_item != NULL) {
+	if (self->allocated >= newsize && self->ob_size < newsize + 16) {
+		assert(self->ob_item != NULL || newsize == 0);
 		self->ob_size = newsize;
 		return 0;
 	}
@@ -2314,6 +2313,11 @@ list_init(PyListObject *self, PyObject *args, PyObject *kw)
 
 	if (!PyArg_ParseTupleAndKeywords(args, kw, "|O:list", kwlist, &arg))
 		return -1;
+
+	/* Verify list invariants established by PyType_GenericAlloc() */
+	assert(0 <= self->ob_size  &&  self->ob_size <= self->allocated);
+	assert(self->ob_item != NULL  ||  self->allocated == 0);
+
 	/* Empty previous contents */
 	if (self->ob_item != NULL) {
 		(void)list_clear(self);