Added checks to prevent PyUnicode_Count() from dumping core

in case the parameters are out of bounds and fixes error handling
for .count(), .startswith() and .endswith() for the case of
mixed string/Unicode objects.

This patch adds Python style index semantics to PyUnicode_Count()
indices (including the special handling of negative indices).

The patch is an extended version of patch #103249 submitted
by Michael Hudson (mwh) on SF. It also includes new test cases.

Lib/test/string_tests.py

@@ -53,6 +53,10 @@ def run_method_tests(test):
 
     test('capitalize', ' hello ', ' hello ')
     test('capitalize', 'hello ', 'Hello ')
+
+    test('count', 'aaa', 3, 'a')
+    test('count', 'aaa', 0, 'b')
+    
     test('find', 'abcdefghiabc', 0, 'abc')
     test('find', 'abcdefghiabc', 9, 'abc', 1)
     test('find', 'abcdefghiabc', -1, 'def', 4)

Lib/test/test_unicode.py

@@ -32,6 +32,13 @@ def test(method, input, output, *args):
 test('capitalize', u' hello ', u' hello ')
 test('capitalize', u'hello ', u'Hello ')
 
+test('count', u'aaa', 3, u'a')
+test('count', u'aaa', 0, u'b')
+test('count', 'aaa', 3, u'a')
+test('count', 'aaa', 0, u'b')
+test('count', u'aaa', 3, 'a')
+test('count', u'aaa', 0, 'b')
+
 test('title', u' hello ', u' Hello ')
 test('title', u'hello ', u'Hello ')
 test('title', u"fOrMaT thIs aS titLe String", u'Format This As Title String')

Objects/stringobject.c

@@ -1236,9 +1236,14 @@ string_count(PyStringObject *self, PyObject *args)
 		sub = PyString_AS_STRING(subobj);
 		n = PyString_GET_SIZE(subobj);
 	}
-	else if (PyUnicode_Check(subobj))
+	else if (PyUnicode_Check(subobj)) {
-		return PyInt_FromLong(
+		int count;
-		        PyUnicode_Count((PyObject *)self, subobj, i, last));
+		count = PyUnicode_Count((PyObject *)self, subobj, i, last);
+		if (count == -1)
+			return NULL;
+		else
+		    	return PyInt_FromLong((long) count);
+	}
 	else if (PyObject_AsCharBuffer(subobj, &sub, &n))
 		return NULL;
 
@@ -1637,10 +1642,15 @@ string_startswith(PyStringObject *self, PyObject *args)
 		prefix = PyString_AS_STRING(subobj);
 		plen = PyString_GET_SIZE(subobj);
 	}
-	else if (PyUnicode_Check(subobj))
+	else if (PyUnicode_Check(subobj)) {
-		return PyInt_FromLong(
+	    	int rc;
-		        PyUnicode_Tailmatch((PyObject *)self, 
+		rc = PyUnicode_Tailmatch((PyObject *)self, 
-					    subobj, start, end, -1));
+					  subobj, start, end, -1);
+		if (rc == -1)
+			return NULL;
+		else
+			return PyInt_FromLong((long) rc);
+	}
 	else if (PyObject_AsCharBuffer(subobj, &prefix, &plen))
 		return NULL;
 
@@ -1690,10 +1700,15 @@ string_endswith(PyStringObject *self, PyObject *args)
 		suffix = PyString_AS_STRING(subobj);
 		slen = PyString_GET_SIZE(subobj);
 	}
-	else if (PyUnicode_Check(subobj))
+	else if (PyUnicode_Check(subobj)) {
-		return PyInt_FromLong(
+	    	int rc;
-		        PyUnicode_Tailmatch((PyObject *)self, 
+		rc = PyUnicode_Tailmatch((PyObject *)self, 
-					    subobj, start, end, +1));
+					  subobj, start, end, +1);
+		if (rc == -1)
+			return NULL;
+		else
+			return PyInt_FromLong((long) rc);
+	}
 	else if (PyObject_AsCharBuffer(subobj, &suffix, &slen))
 		return NULL;
 

Objects/unicodeobject.c

@@ -2392,6 +2392,17 @@ int count(PyUnicodeObject *self,
 {
     int count = 0;
 
+    if (start < 0)
+        start += self->length;
+    if (start < 0)
+        start = 0;
+    if (end > self->length)
+        end = self->length;
+    if (end < 0)
+        end += self->length;
+    if (end < 0)
+        end = 0;
+
     if (substring->length == 0)
 	return (end - start + 1);