Index: Objects/unicodeobject.c
===================================================================
--- Objects/unicodeobject.c	(revisión: 58710)
+++ Objects/unicodeobject.c	(copia de trabajo)
@@ -6027,6 +6027,46 @@
     return (PyObject*) u;
 }
 
+/*
+This function is a helper for the "find" family (find, rfind, index,
+rindex), because they all have the same behaviour for the arguments.
+
+It does not touch the variables received until it knows everything 
+is ok.
+*/
+
+int 
+_ParseTupleFinds (PyObject *args, PyObject **substring, 
+                  Py_ssize_t *start, Py_ssize_t *end) {
+    PyObject *tmp_substring;
+    Py_ssize_t tmp_start = 0;
+    Py_ssize_t tmp_end = PY_SSIZE_T_MAX;
+    PyObject *obj_start=Py_None, *obj_end=Py_None;
+
+    if (!PyArg_ParseTuple(args, "O|OO:find", &tmp_substring,
+         &obj_start, &obj_end))
+        return 0;
+
+    /* To support None in "start" and "end" arguments, meaning
+       the same as if they were not passed.
+    */
+    if (obj_start != Py_None)
+        if (!_PyEval_SliceIndex(obj_start, &tmp_start))
+            return 0;
+    if (obj_end != Py_None)
+        if (!_PyEval_SliceIndex(obj_end, &tmp_end))
+            return 0;
+
+    tmp_substring = PyUnicode_FromObject(tmp_substring);
+    if (!tmp_substring)
+        return 0;
+
+    *start = tmp_start;
+    *end = tmp_end;
+    *substring = tmp_substring;
+    return 1;
+}
+
 PyDoc_STRVAR(find__doc__,
 "S.find(sub [,start [,end]]) -> int\n\
 \n\
@@ -6040,16 +6080,12 @@
 unicode_find(PyUnicodeObject *self, PyObject *args)
 {
     PyObject *substring;
-    Py_ssize_t start = 0;
-    Py_ssize_t end = PY_SSIZE_T_MAX;
+    Py_ssize_t start;
+    Py_ssize_t end;
     Py_ssize_t result;
 
-    if (!PyArg_ParseTuple(args, "O|O&O&:find", &substring,
-		_PyEval_SliceIndex, &start, _PyEval_SliceIndex, &end))
+    if (!_ParseTupleFinds(args, &substring, &start, &end))
         return NULL;
-    substring = PyUnicode_FromObject(substring);
-    if (!substring)
-	return NULL;
 
     result = stringlib_find_slice(
         PyUnicode_AS_UNICODE(self), PyUnicode_GET_SIZE(self),
@@ -6110,15 +6146,11 @@
 {
     Py_ssize_t result;
     PyObject *substring;
-    Py_ssize_t start = 0;
-    Py_ssize_t end = PY_SSIZE_T_MAX;
+    Py_ssize_t start;
+    Py_ssize_t end;
 
-    if (!PyArg_ParseTuple(args, "O|O&O&:index", &substring,
-		_PyEval_SliceIndex, &start, _PyEval_SliceIndex, &end))
+    if (!_ParseTupleFinds(args, &substring, &start, &end))
         return NULL;
-    substring = PyUnicode_FromObject(substring);
-    if (!substring)
-	return NULL;
 
     result = stringlib_find_slice(
         PyUnicode_AS_UNICODE(self), PyUnicode_GET_SIZE(self),
@@ -6781,16 +6813,12 @@
 unicode_rfind(PyUnicodeObject *self, PyObject *args)
 {
     PyObject *substring;
-    Py_ssize_t start = 0;
-    Py_ssize_t end = PY_SSIZE_T_MAX;
+    Py_ssize_t start;
+    Py_ssize_t end;
     Py_ssize_t result;
 
-    if (!PyArg_ParseTuple(args, "O|O&O&:rfind", &substring,
-		_PyEval_SliceIndex, &start, _PyEval_SliceIndex, &end))
-        return NULL;
-    substring = PyUnicode_FromObject(substring);
-    if (!substring)
-	return NULL;
+    if (!_ParseTupleFinds(args, &substring, &start, &end))
+	    return NULL;
 
     result = stringlib_rfind_slice(
         PyUnicode_AS_UNICODE(self), PyUnicode_GET_SIZE(self),
@@ -6812,16 +6840,12 @@
 unicode_rindex(PyUnicodeObject *self, PyObject *args)
 {
     PyObject *substring;
-    Py_ssize_t start = 0;
-    Py_ssize_t end = PY_SSIZE_T_MAX;
+    Py_ssize_t start;
+    Py_ssize_t end;
     Py_ssize_t result;
 
-    if (!PyArg_ParseTuple(args, "O|O&O&:rindex", &substring,
-		_PyEval_SliceIndex, &start, _PyEval_SliceIndex, &end))
-        return NULL;
-    substring = PyUnicode_FromObject(substring);
-    if (!substring)
-	return NULL;
+    if (!_ParseTupleFinds(args, &substring, &start, &end))
+	    return NULL;
 
     result = stringlib_rfind_slice(
         PyUnicode_AS_UNICODE(self), PyUnicode_GET_SIZE(self),
Index: Objects/stringobject.c
===================================================================
--- Objects/stringobject.c	(revisión: 58710)
+++ Objects/stringobject.c	(copia de trabajo)
@@ -1879,16 +1879,28 @@
 	const char *sub;
 	Py_ssize_t sub_len;
 	Py_ssize_t start=0, end=PY_SSIZE_T_MAX;
+	PyObject *obj_start=Py_None, *obj_end=Py_None;
 
-	if (!PyArg_ParseTuple(args, "O|O&O&:find/rfind/index/rindex", &subobj,
-		_PyEval_SliceIndex, &start, _PyEval_SliceIndex, &end))
+	if (!PyArg_ParseTuple(args, "O|OO:find/rfind/index/rindex", &subobj,
+		&obj_start, &obj_end))
 		return -2;
+	/* To support None in "start" and "end" arguments, meaning
+	   the same as if they were not passed.
+	*/
+	if (obj_start != Py_None)
+		if (!_PyEval_SliceIndex(obj_start, &start))
+	        return -2;
+	if (obj_end != Py_None)
+		if (!_PyEval_SliceIndex(obj_end, &end))
+	        return -2;
+
 	if (PyString_Check(subobj)) {
 		sub = PyString_AS_STRING(subobj);
 		sub_len = PyString_GET_SIZE(subobj);
 	}
+
 #ifdef Py_USING_UNICODE
-	else if (PyUnicode_Check(subobj))
+	else if (PyUnicode_Check(subobj)) 
 		return PyUnicode_Find(
 			(PyObject *)self, subobj, start, end, dir);
 #endif
Index: Lib/test/string_tests.py
===================================================================
--- Lib/test/string_tests.py	(revisión: 58710)
+++ Lib/test/string_tests.py	(copia de trabajo)
@@ -159,6 +159,13 @@
         self.checkequal(3, 'abc', 'find', '', 3)
         self.checkequal(-1, 'abc', 'find', '', 4)
 
+        # to check the ability to pass None as defaults
+        self.checkequal( 2, 'rrarrrrrrrrra', 'find', 'a')
+        self.checkequal(12, 'rrarrrrrrrrra', 'find', 'a', 4)
+        self.checkequal(-1, 'rrarrrrrrrrra', 'find', 'a', 4, 6)
+        self.checkequal(12, 'rrarrrrrrrrra', 'find', 'a', 4, None)
+        self.checkequal( 2, 'rrarrrrrrrrra', 'find', 'a', None, 6)
+
         self.checkraises(TypeError, 'hello', 'find')
         self.checkraises(TypeError, 'hello', 'find', 42)
 
@@ -197,6 +204,13 @@
         self.checkequal(3, 'abc', 'rfind', '', 3)
         self.checkequal(-1, 'abc', 'rfind', '', 4)
 
+        # to check the ability to pass None as defaults
+        self.checkequal(12, 'rrarrrrrrrrra', 'rfind', 'a')
+        self.checkequal(12, 'rrarrrrrrrrra', 'rfind', 'a', 4)
+        self.checkequal(-1, 'rrarrrrrrrrra', 'rfind', 'a', 4, 6)
+        self.checkequal(12, 'rrarrrrrrrrra', 'rfind', 'a', 4, None)
+        self.checkequal( 2, 'rrarrrrrrrrra', 'rfind', 'a', None, 6)
+
         self.checkraises(TypeError, 'hello', 'rfind')
         self.checkraises(TypeError, 'hello', 'rfind', 42)
 
@@ -211,6 +225,13 @@
         self.checkraises(ValueError, 'abcdefghi', 'index', 'ghi', 8)
         self.checkraises(ValueError, 'abcdefghi', 'index', 'ghi', -1)
 
+        # to check the ability to pass None as defaults
+        self.checkequal( 2, 'rrarrrrrrrrra', 'index', 'a')
+        self.checkequal(12, 'rrarrrrrrrrra', 'index', 'a', 4)
+        self.checkraises(ValueError, 'rrarrrrrrrrra', 'index', 'a', 4, 6)
+        self.checkequal(12, 'rrarrrrrrrrra', 'index', 'a', 4, None)
+        self.checkequal( 2, 'rrarrrrrrrrra', 'index', 'a', None, 6)
+
         self.checkraises(TypeError, 'hello', 'index')
         self.checkraises(TypeError, 'hello', 'index', 42)
 
@@ -226,6 +247,13 @@
         self.checkraises(ValueError, 'abcdefghi', 'rindex', 'ghi', 0, 8)
         self.checkraises(ValueError, 'abcdefghi', 'rindex', 'ghi', 0, -1)
 
+        # to check the ability to pass None as defaults
+        self.checkequal(12, 'rrarrrrrrrrra', 'rindex', 'a')
+        self.checkequal(12, 'rrarrrrrrrrra', 'rindex', 'a', 4)
+        self.checkraises(ValueError, 'rrarrrrrrrrra', 'rindex', 'a', 4, 6)
+        self.checkequal(12, 'rrarrrrrrrrra', 'rindex', 'a', 4, None)
+        self.checkequal( 2, 'rrarrrrrrrrra', 'rindex', 'a', None, 6)
+
         self.checkraises(TypeError, 'hello', 'rindex')
         self.checkraises(TypeError, 'hello', 'rindex', 42)