Add ability to specify output format for DurationField

docs/api-guide/settings.md

@@ -317,11 +317,11 @@ Default: `['iso-8601']`
 
 #### DURATION_FORMAT
 
-A format string that should be used by default for rendering the output of `DurationField` serializer fields.  If `None`, then `DurationField` serializer fields will return Python `timedelta` objects, and the duration encoding will be determined by the renderer.
+Indicates the default format thath should be used for rendering the output of `DurationField` serializer fields.  If `None`, then `DurationField` serializer fields will return Python `timedelta` objects, and the duration encoding will be determined by the renderer.
 
-May be any of `None`, `'iso-8601'` or `'standard'` (the format accepted by `django.utils.dateparse.parse_duration`).
+May be any of `None`, `'iso-8601'` or `'django'` (the format accepted by `django.utils.dateparse.parse_duration`).
 
-Default: `'standard'`
+Default: `'django'`
 
 ---
 

rest_framework/fields.py

@@ -1357,11 +1357,16 @@ def __init__(self, *, format=empty, **kwargs):
         if format is not empty:
             if format is None or (isinstance(format, str) and format.lower() in (ISO_8601, DJANGO_DURATION_FORMAT)):
                 self.format = format
-            else:
+            elif isinstance(format, str):
                 raise ValueError(
                     f"Unknown duration format provided, got '{format}'"
                     " while expecting 'django', 'iso-8601' or `None`."
                 )
+            else:
+                raise TypeError(
+                    "duration format must be either str or `None`,"
+                    f" not {type(format).__name__}"
+                )
         super().__init__(**kwargs)
         if self.max_value is not None:
             message = lazy_format(self.error_messages['max_value'], max_value=self.max_value)
@@ -1396,9 +1401,13 @@ def to_representation(self, value):
             if output_format.lower() == DJANGO_DURATION_FORMAT:
                 return duration_string(value)
 
-        raise ValueError(
-            f"Unknown duration format provided, got '{output_format}'"
-            " while expecting 'django', 'iso-8601' or `None`."
+            raise ValueError(
+                f"Unknown duration format provided, got '{output_format}'"
+                " while expecting 'django', 'iso-8601' or `None`."
+            )
+        raise TypeError(
+            "duration format must be either str or `None`,"
+            f" not {type(output_format).__name__}"
         )
 
 

tests/test_fields.py

@@ -1779,24 +1779,29 @@ def test_invalid_format(self):
             "Unknown duration format provided, got 'unknown'"
             " while expecting 'django', 'iso-8601' or `None`."
         )
-        with pytest.raises(ValueError) as exc_info:
+        with pytest.raises(TypeError) as exc_info:
             serializers.DurationField(format=123)
         assert str(exc_info.value) == (
-            "Unknown duration format provided, got '123'"
-            " while expecting 'django', 'iso-8601' or `None`."
+            "duration format must be either str or `None`, not int"
         )
 
-    @override_settings(REST_FRAMEWORK={'DURATION_FORMAT': 'unknown'})
     def test_invalid_format_in_config(self):
         field = serializers.DurationField()
 
-        with pytest.raises(ValueError) as exc_info:
-            field.to_representation(datetime.timedelta(days=1))
+        with override_settings(REST_FRAMEWORK={'DURATION_FORMAT': 'unknown'}):
+            with pytest.raises(ValueError) as exc_info:
+                field.to_representation(datetime.timedelta(days=1))
 
         assert str(exc_info.value) == (
             "Unknown duration format provided, got 'unknown'"
             " while expecting 'django', 'iso-8601' or `None`."
         )
+        with override_settings(REST_FRAMEWORK={'DURATION_FORMAT': 123}):
+            with pytest.raises(TypeError) as exc_info:
+                field.to_representation(datetime.timedelta(days=1))
+        assert str(exc_info.value) == (
+            "duration format must be either str or `None`, not int"
+        )
 
 
 class TestNoOutputFormatDurationField(FieldValues):