Now in find, rfind, index, and rindex, you can use None as defaults,

as usual with slicing (both with str and unicode strings).  This
fixes issue 1259.

For str only the stringobject.c file was modified.  But for unicode,
I needed to repeat in the four functions a lot of code, so created
a new function that does part of the job for them (and placed it in
find.h, following a suggestion of Barry).

Also added tests for this behaviour.

Lib/test/string_tests.py

@@ -159,6 +159,13 @@ class CommonTest(unittest.TestCase):
         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 @@ class CommonTest(unittest.TestCase):
         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 @@ class CommonTest(unittest.TestCase):
         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 @@ class CommonTest(unittest.TestCase):
         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)
 

Objects/stringlib/find.h

@@ -103,6 +103,53 @@ stringlib_contains_obj(PyObject* str, PyObject* sub)
 
 #endif /* STRINGLIB_STR */
 
+/*
+This function is a helper for the "find" family (find, rfind, index,
+rindex) of unicodeobject.c file, because they all have the same 
+behaviour for the arguments.
+
+It does not touch the variables received until it knows everything 
+is ok.
+
+Note that we receive a pointer to the pointer of the substring object,
+so when we create that object in this function we don't DECREF it,
+because it continues living in the caller functions (those functions, 
+after finishing using the substring, must DECREF it).
+*/
+
+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;
+}
+
+
 #endif /* STRINGLIB_FIND_H */
 
 /*

Objects/stringobject.c

@@ -1880,10 +1880,21 @@ string_find_internal(PyStringObject *self, PyObject *args, int dir)
 	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,
+	if (!PyArg_ParseTuple(args, "O|OO:find/rfind/index/rindex", &subobj,
-		_PyEval_SliceIndex, &start, _PyEval_SliceIndex, &end))
+		&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);

Objects/unicodeobject.c

@@ -6040,16 +6040,12 @@ static PyObject *
 unicode_find(PyUnicodeObject *self, PyObject *args)
 {
     PyObject *substring;
-    Py_ssize_t start = 0;
+    Py_ssize_t start;
-    Py_ssize_t end = PY_SSIZE_T_MAX;
+    Py_ssize_t end;
     Py_ssize_t result;
 
-    if (!PyArg_ParseTuple(args, "O|O&O&:find", &substring,
+    if (!_ParseTupleFinds(args, &substring, &start, &end))
-		_PyEval_SliceIndex, &start, _PyEval_SliceIndex, &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 +6106,11 @@ unicode_index(PyUnicodeObject *self, PyObject *args)
 {
     Py_ssize_t result;
     PyObject *substring;
-    Py_ssize_t start = 0;
+    Py_ssize_t start;
-    Py_ssize_t end = PY_SSIZE_T_MAX;
+    Py_ssize_t end;
 
-    if (!PyArg_ParseTuple(args, "O|O&O&:index", &substring,
+    if (!_ParseTupleFinds(args, &substring, &start, &end))
-		_PyEval_SliceIndex, &start, _PyEval_SliceIndex, &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 +6773,12 @@ static PyObject *
 unicode_rfind(PyUnicodeObject *self, PyObject *args)
 {
     PyObject *substring;
-    Py_ssize_t start = 0;
+    Py_ssize_t start;
-    Py_ssize_t end = PY_SSIZE_T_MAX;
+    Py_ssize_t end;
     Py_ssize_t result;
 
-    if (!PyArg_ParseTuple(args, "O|O&O&:rfind", &substring,
+    if (!_ParseTupleFinds(args, &substring, &start, &end))
-		_PyEval_SliceIndex, &start, _PyEval_SliceIndex, &end))
+	    return NULL;
-        return NULL;
-    substring = PyUnicode_FromObject(substring);
-    if (!substring)
-	return NULL;
 
     result = stringlib_rfind_slice(
         PyUnicode_AS_UNICODE(self), PyUnicode_GET_SIZE(self),
@@ -6812,16 +6800,12 @@ static PyObject *
 unicode_rindex(PyUnicodeObject *self, PyObject *args)
 {
     PyObject *substring;
-    Py_ssize_t start = 0;
+    Py_ssize_t start;
-    Py_ssize_t end = PY_SSIZE_T_MAX;
+    Py_ssize_t end;
     Py_ssize_t result;
 
-    if (!PyArg_ParseTuple(args, "O|O&O&:rindex", &substring,
+    if (!_ParseTupleFinds(args, &substring, &start, &end))
-		_PyEval_SliceIndex, &start, _PyEval_SliceIndex, &end))
+	    return NULL;
-        return NULL;
-    substring = PyUnicode_FromObject(substring);
-    if (!substring)
-	return NULL;
 
     result = stringlib_rfind_slice(
         PyUnicode_AS_UNICODE(self), PyUnicode_GET_SIZE(self),