SF bug #1054139: serious string hashing error in 2.4b1

rhettinger · rhettinger · commit 561fbf138d30 · 2004-10-26T01:52:37.000Z
_PyString_Resize() readied strings for mutation but did not invalidate
the cached hash value.
diff --git a/Lib/test/string_tests.py b/Lib/test/string_tests.py
@@ -80,6 +80,15 @@ def checkcall(self, object, methodname, *args):
         args = self.fixtype(args)
         getattr(object, methodname)(*args)
 
+    def test_hash(self):
+        # SF bug 1054139:  += optimization was not invalidating cached hash value
+        a = self.type2test('DNSSEC')
+        b = self.type2test('')
+        for c in a:
+            b += c
+            hash(b)
+        self.assertEqual(hash(a), hash(b))
+
     def test_capitalize(self):
         self.checkequal(' hello ', ' hello ', 'capitalize')
         self.checkequal('Hello ', 'Hello ','capitalize')
diff --git a/Misc/NEWS b/Misc/NEWS
@@ -32,7 +32,7 @@ License Version 2.
 Core and builtins
 -----------------
 
-...
+- Bug #1054139 _PyString_Resize() now invalidates its cached hash value.
 
 Extension Modules
 -----------------
diff --git a/Objects/stringobject.c b/Objects/stringobject.c
@@ -3530,6 +3530,7 @@ _PyString_Resize(PyObject **pv, int newsize)
 	sv = (PyStringObject *) *pv;
 	sv->ob_size = newsize;
 	sv->ob_sval[newsize] = '\0';
+	sv->ob_shash = -1;	/* invalidate cached hash value */
 	return 0;
 }
 

Original file line number	Diff line number	Diff line change
`@@ -3530,6 +3530,7 @@ _PyString_Resize(PyObject **pv, int newsize)`
`3530`	`3530`	`sv = (PyStringObject ) pv;`
`3531`	`3531`	`sv->ob_size = newsize;`
`3532`	`3532`	`sv->ob_sval[newsize] = '\0';`
	`3533`	`+ sv->ob_shash = -1; /* invalidate cached hash value */`
`3533`	`3534`	`return 0;`
`3534`	`3535`	`}`
`3535`	`3536`