          expected = dedent("""
              TestSerializer():
                  id = IntegerField(label='ID', read_only=True)
                  duration_field = DurationField(max_value=datetime.timedelta(3), min_value=datetime.timedelta(1))
          """)
          self.assertEqual(unicode_repr(TestSerializer()), expected)
  
  
  class TestGenericIPAddressFieldValidation(TestCase):
      def test_ip_address_validation(self):
 
</s> remove        {py34,py35,py36}-django20,
       {py35,py36}-django21
       {py35,py36}-djangomaster,
 </s> add        {py34,py35,py36,py37}-django20,
       {py35,py36,py37}-django21
       {py35,py36,py37}-djangomaster, </s> remove       - env: DJANGO=2.1
 </s> add 
        """) if sys.version_info < (3, 7) else dedent("""
            TestSerializer():
                id = IntegerField(label='ID', read_only=True)
                duration_field = DurationField(max_value=datetime.timedelta(days=3), min_value=datetime.timedelta(days=1))
          expected = dedent("""
              TestSerializer():
                  id = IntegerField(label='ID', read_only=True)
                  duration_field = DurationField(max_value=datetime.timedelta(3), min_value=datetime.timedelta(1))
        """) if sys.version_info < (3, 7) else dedent("""
            TestSerializer():
                id = IntegerField(label='ID', read_only=True)
                duration_field = DurationField(max_value=datetime.timedelta(days=3), min_value=datetime.timedelta(days=1))
          """)
          self.assertEqual(unicode_repr(TestSerializer()), expected)
  
  
  class TestGenericIPAddressFieldValidation(TestCase):
      def test_ip_address_validation(self):
keep keep keep add keep keep keep keep keep keep
 Add Python 3.7 support (#6141) 
tests/test_model_serializer.py