Replace f-strings with format for py35 compatability

Author: tim-mccurrach

rest_framework/response.py

@@ -49,7 +49,7 @@ def __init__(
         self.exception = exception
         self.content_type = content_type
         if reason:
-            self.reason_phrase = f"{self.status_text} ({reason})"
+            self.reason_phrase = "{} ({})".format(self.status_text, reason)
 
         if headers:
             for name, value in headers.items():

tests/test_response.py

@@ -297,7 +297,7 @@ def test_form_has_label_and_help_text(self):
 class ReasonPhraseTests(TestCase):
     def test_reason_is_set(self):
         resp = self.client.get('/with_reason')
-        self.assertEqual(f"OK ({DUMMYREASON})", resp.reason_phrase)
+        self.assertEqual("OK ({})".format(DUMMYREASON), resp.reason_phrase)
 
     def test_reason_phrase_with_no_reason(self):
         resp = self.client.get('/')

tests/test_views.py

@@ -99,7 +99,7 @@ def test_400_validation_error(self):
         request = factory.get('/')
         response = ValidationErrorView.as_view()(request)
         assert response.status_code == status.HTTP_400_BAD_REQUEST
-        assert response.reason_phrase == f"{STATUS_CODE_400} ({VALIDATION_ERROR})"
+        assert response.reason_phrase == "{} ({})".format(STATUS_CODE_400, VALIDATION_ERROR)
         assert response.data == [VALIDATION_ERROR]
 
 
@@ -119,7 +119,7 @@ def test_400_validation_error(self):
         request = factory.get('/')
         response = validation_error_view(request)
         assert response.status_code == status.HTTP_400_BAD_REQUEST
-        assert response.reason_phrase == f"{STATUS_CODE_400} ({VALIDATION_ERROR})"
+        assert response.reason_phrase == "{} ({})".format(STATUS_CODE_400, VALIDATION_ERROR)
         assert response.data == [VALIDATION_ERROR]