python · mjpieters · Feb 12, 2017 · Feb 14, 2017
diff --git a/Doc/tools/extensions/pyspecific.py b/Doc/tools/extensions/pyspecific.py
@@ -34,7 +34,7 @@
 
 
 ISSUE_URI = 'https://bugs.python.org/issue%s'
-SOURCE_URI = 'https://hg.python.org/cpython/file/3.6/%s'
+SOURCE_URI = 'https://github.com/python/cpython/tree/3.6/%s'
 
 # monkey-patch reST parser to disable alphabetic and roman enumerated lists
 from docutils.parsers.rst.states import Body
@@ -79,7 +79,7 @@ def new_depart_literal_block(self, node):
 
 def issue_role(typ, rawtext, text, lineno, inliner, options={}, content=[]):
     issue = utils.unescape(text)
-    text = 'issue ' + issue
+    text = 'bpo-' + issue
     refnode = nodes.reference(text, text, refuri=ISSUE_URI % issue)
     return [refnode], []
 
@@ -225,7 +225,7 @@ def run(self):
 
 # Support for including Misc/NEWS
 
-issue_re = re.compile('([Ii])ssue #([0-9]+)')
+issue_re = re.compile('(?:[Ii]ssue #|bpo-)([0-9]+)')
 whatsnew_re = re.compile(r"(?im)^what's new in (.*?)\??$")
 
 
@@ -253,7 +253,7 @@ def run(self):
             text = 'The NEWS file is not available.'
             node = nodes.strong(text, text)
             return [node]
-        content = issue_re.sub(r'`\1ssue #\2 <https://bugs.python.org/\2>`__',
+        content = issue_re.sub(r'`bpo-\1 <https://bugs.python.org/issue\1>`__',
                                content)
         content = whatsnew_re.sub(r'\1', content)
         # remove first 3 lines as they are the main heading

diff --git a/Lib/test/test_unicode.py b/Lib/test/test_unicode.py
@@ -1448,6 +1448,15 @@ def test_formatting_huge_precision(self):
         with self.assertRaises(ValueError):
             result = format_string % 2.34
 
+    def test_issue28598_strsubclass_rhs(self):
+        # A subclass of str with an __rmod__ method should be able to hook
+        # into the % operator
+        class SubclassedStr(str):
+            def __rmod__(self, other):
+                return 'Success, self.__rmod__({!r}) was called'.format(other)
+        self.assertEqual('lhs %% %r' % SubclassedStr('rhs'),
+                         "Success, self.__rmod__('lhs %% %r') was called")
+
     @support.cpython_only
     def test_formatting_huge_precision_c_limits(self):
         from _testcapi import INT_MAX

diff --git a/Misc/NEWS b/Misc/NEWS
@@ -10,6 +10,9 @@ What's New in Python 3.6.1 release candidate 1?
 Core and Builtins
 -----------------
 
+- Issue #28598: Support __rmod__ for subclasses of str being called before
+  str.__mod__. Patch by Martijn Pieters.
+
 - Issue #29319: Prevent RunMainFromImporter overwriting sys.path[0].
 
 - Issue #29337: Fixed possible BytesWarning when compare the code objects.

diff --git a/Python/ceval.c b/Python/ceval.c
@@ -1409,9 +1409,15 @@ _PyEval_EvalFrameDefault(PyFrameObject *f, int throwflag)
         TARGET(BINARY_MODULO) {
             PyObject *divisor = POP();
             PyObject *dividend = TOP();
-            PyObject *res = PyUnicode_CheckExact(dividend) ?
-                PyUnicode_Format(dividend, divisor) :
-                PyNumber_Remainder(dividend, divisor);
+            PyObject *res;
+            if (PyUnicode_CheckExact(dividend) && (
+                  !PyUnicode_Check(divisor) || PyUnicode_CheckExact(divisor))) {
+              // fast path; string formatting, but not if the RHS is a str subclass
+              // (see issue28598)
+              res = PyUnicode_Format(dividend, divisor);
+            } else {
+              res = PyNumber_Remainder(dividend, divisor);
+            }
             Py_DECREF(divisor);
             Py_DECREF(dividend);
             SET_TOP(res);