Fix str.rpartition(sep) when sep is not found in str.

Partially from SF patch #1551339, but also taken from head.

Doc/lib/libstdtypes.tex

@@ -771,8 +771,8 @@ The original string is returned if
 Split the string at the last occurrence of \var{sep}, and return
 a 3-tuple containing the part before the separator, the separator
 itself, and the part after the separator.  If the separator is not
-found, return a 3-tuple containing the string itself, followed by
+found, return a 3-tuple containing two empty strings, followed by
-two empty strings.
+the string itself.
 \versionadded{2.5}
 \end{methoddesc}
 

Lib/test/string_tests.py

@@ -1069,7 +1069,7 @@ class MixinStrUnicodeUserStringTest:
         # from raymond's original specification
         S = 'http://www.python.org'
         self.checkequal(('http', '://', 'www.python.org'), S, 'rpartition', '://')
-        self.checkequal(('http://www.python.org', '', ''), S, 'rpartition', '?')
+        self.checkequal(('', '', 'http://www.python.org'), S, 'rpartition', '?')
         self.checkequal(('', 'http://', 'www.python.org'), S, 'rpartition', 'http://')
         self.checkequal(('http://www.python.', 'org', ''), S, 'rpartition', 'org')
 

Misc/NEWS

@@ -27,6 +27,9 @@ Core and builtins
 
 - Patch #1546288: fix seg fault in dict_equal due to ref counting bug.
 
+- The return tuple from str.rpartition(sep) is (tail, sep, head) where
+  head is the original string if sep was not found.
+
 
 Library
 -------

Objects/stringlib/partition.h

@@ -78,12 +78,12 @@ stringlib_rpartition(
             }
 
     if (pos < 0) {
-	Py_INCREF(str_obj);
+	Py_INCREF(STRINGLIB_EMPTY);
-	PyTuple_SET_ITEM(out, 0, (PyObject*) str_obj);
+	PyTuple_SET_ITEM(out, 0, (PyObject*) STRINGLIB_EMPTY);
 	Py_INCREF(STRINGLIB_EMPTY);
 	PyTuple_SET_ITEM(out, 1, (PyObject*) STRINGLIB_EMPTY);
-	Py_INCREF(STRINGLIB_EMPTY);
+	Py_INCREF(str_obj);        
-	PyTuple_SET_ITEM(out, 2, (PyObject*) STRINGLIB_EMPTY);
+	PyTuple_SET_ITEM(out, 2, (PyObject*) str_obj);
 	return out;
     }
 

Objects/stringobject.c

@@ -1543,11 +1543,11 @@ string_partition(PyStringObject *self, PyObject *sep_obj)
 }
 
 PyDoc_STRVAR(rpartition__doc__,
-"S.rpartition(sep) -> (head, sep, tail)\n\
+"S.rpartition(sep) -> (tail, sep, head)\n\
 \n\
 Searches for the separator sep in S, starting at the end of S, and returns\n\
 the part before it, the separator itself, and the part after it.  If the\n\
-separator is not found, returns S and two empty strings.");
+separator is not found, returns two empty strings and S.");
 
 static PyObject *
 string_rpartition(PyStringObject *self, PyObject *sep_obj)

Objects/unicodeobject.c

@@ -6708,11 +6708,11 @@ unicode_partition(PyUnicodeObject *self, PyObject *separator)
 }
 
 PyDoc_STRVAR(rpartition__doc__,
-"S.rpartition(sep) -> (head, sep, tail)\n\
+"S.rpartition(sep) -> (tail, sep, head)\n\
 \n\
 Searches for the separator sep in S, starting at the end of S, and returns\n\
 the part before it, the separator itself, and the part after it.  If the\n\
-separator is not found, returns S and two empty strings.");
+separator is not found, returns two empty strings and S.");
 
 static PyObject*
 unicode_rpartition(PyUnicodeObject *self, PyObject *separator)