fix rmod

Doc/library/collections.rst

@@ -1252,6 +1252,3 @@ attribute.
     .. versionchanged:: 3.5
        New methods ``__getnewargs__``, ``__rmod__``, ``casefold``,
        ``format_map``, ``isprintable``, and ``maketrans``.
-
-    .. versionchanged:: 3.8
-        The ``__rmod__`` method is removed.

Lib/collections/__init__.py

@@ -1214,6 +1214,10 @@ class UserString(_collections_abc.Sequence):
     __rmul__ = __mul__
     def __mod__(self, args):
         return self.__class__(self.data % args)
+    def __rmod__(self, template):
+        if isinstance(template, str):
+            return self.__class__(template % self)
+        return NotImplemented
     # the following methods are defined in alphabetical order:
     def capitalize(self): return self.__class__(self.data.capitalize())
     def casefold(self):

Lib/test/test_collections.py

@@ -70,6 +70,11 @@ class TestUserObjects(unittest.TestCase):
         obj[123] = "abc"
         self._copy_test(obj)
 
+    def test_str_rmod(self):
+        arg = UserString("python")
+        template = "I love %s"
+        self.assertEqual(arg.__rmod__(template), "I love python")
+        self.assertIs(arg.__rmod__(type('Dummy', (), {})), NotImplemented)
 
 ################################################################################
 ### ChainMap (helper class for configparser and the string module)

Misc/NEWS.d/next/Library/2019-05-14-21-39-52.bpo-25652.xLw42k.rst

-The ``__rmod__`` method of ``collections.UserString`` class is removed.
+Fix bug in ``__rmod__`` of ``UserString`` - by Batuhan Taskaya.