[1.11.x] Fixed #28502 -- Made stringformat template filter accept tuples.

Backport of 4ead705cb3 and
ed77bea582 from master

django/template/defaultfilters.py

@@ -249,6 +249,8 @@ def stringformat(value, arg):
     See https://docs.python.org/3/library/stdtypes.html#printf-style-string-formatting
     for documentation of Python string formatting.
     """
+    if isinstance(value, tuple):
+        value = six.text_type(value)
     try:
         return ("%" + six.text_type(arg)) % value
     except (ValueError, TypeError):

docs/releases/1.11.5.txt

@@ -13,3 +13,5 @@ Bugfixes
   in GEOS 3.6.2) (:ticket:`28441`).
 
 * Fixed test database creation with ``cx_Oracle`` 6 (:ticket:`28498`).
+
+* Fixed select widget rendering when option values are tuples (:ticket:`28502`).

tests/template_tests/filter_tests/test_stringformat.py

@@ -29,6 +29,9 @@ class FunctionTests(SimpleTestCase):
 
     def test_format(self):
         self.assertEqual(stringformat(1, '03d'), '001')
+        self.assertEqual(stringformat((1, 2, 3), 's'), '(1, 2, 3)')
+        self.assertEqual(stringformat((1,), 's'), '(1,)')
 
     def test_invalid(self):
         self.assertEqual(stringformat(1, 'z'), '')
+        self.assertEqual(stringformat((1, 2, 3), 'd'), '')