Make Field constructors keyword-only

rest_framework/fields.py

@@ -320,7 +320,7 @@ class Field:
     default_empty_html = empty
     initial = None
 
-    def __init__(self, read_only=False, write_only=False,
+    def __init__(self, *, read_only=False, write_only=False,
                  required=None, default=empty, initial=empty, source=None,
                  label=None, help_text=None, style=None,
                  error_messages=None, validators=None, allow_null=False):
@@ -1161,14 +1161,14 @@ class DateTimeField(Field):
     }
     datetime_parser = datetime.datetime.strptime
 
-    def __init__(self, format=empty, input_formats=None, default_timezone=None, *args, **kwargs):
+    def __init__(self, format=empty, input_formats=None, default_timezone=None, **kwargs):
         if format is not empty:
             self.format = format
         if input_formats is not None:
             self.input_formats = input_formats
         if default_timezone is not None:
             self.timezone = default_timezone
-        super().__init__(*args, **kwargs)
+        super().__init__(**kwargs)
 
     def enforce_timezone(self, value):
         """
@@ -1247,12 +1247,12 @@ class DateField(Field):
     }
     datetime_parser = datetime.datetime.strptime
 
-    def __init__(self, format=empty, input_formats=None, *args, **kwargs):
+    def __init__(self, format=empty, input_formats=None, **kwargs):
         if format is not empty:
             self.format = format
         if input_formats is not None:
             self.input_formats = input_formats
-        super().__init__(*args, **kwargs)
+        super().__init__(**kwargs)
 
     def to_internal_value(self, value):
         input_formats = getattr(self, 'input_formats', api_settings.DATE_INPUT_FORMATS)
@@ -1313,12 +1313,12 @@ class TimeField(Field):
     }
     datetime_parser = datetime.datetime.strptime
 
-    def __init__(self, format=empty, input_formats=None, *args, **kwargs):
+    def __init__(self, format=empty, input_formats=None, **kwargs):
         if format is not empty:
             self.format = format
         if input_formats is not None:
             self.input_formats = input_formats
-        super().__init__(*args, **kwargs)
+        super().__init__(**kwargs)
 
     def to_internal_value(self, value):
         input_formats = getattr(self, 'input_formats', api_settings.TIME_INPUT_FORMATS)
@@ -1468,9 +1468,9 @@ class MultipleChoiceField(ChoiceField):
     }
     default_empty_html = []
 
-    def __init__(self, *args, **kwargs):
+    def __init__(self, **kwargs):
         self.allow_empty = kwargs.pop('allow_empty', True)
-        super().__init__(*args, **kwargs)
+        super().__init__(**kwargs)
 
     def get_value(self, dictionary):
         if self.field_name not in dictionary:
@@ -1527,12 +1527,12 @@ class FileField(Field):
         'max_length': _('Ensure this filename has at most {max_length} characters (it has {length}).'),
     }
 
-    def __init__(self, *args, **kwargs):
+    def __init__(self, **kwargs):
         self.max_length = kwargs.pop('max_length', None)
         self.allow_empty_file = kwargs.pop('allow_empty_file', False)
         if 'use_url' in kwargs:
             self.use_url = kwargs.pop('use_url')
-        super().__init__(*args, **kwargs)
+        super().__init__(**kwargs)
 
     def to_internal_value(self, data):
         try:
@@ -1576,9 +1576,9 @@ class ImageField(FileField):
         ),
     }
 
-    def __init__(self, *args, **kwargs):
+    def __init__(self, **kwargs):
         self._DjangoImageField = kwargs.pop('_DjangoImageField', DjangoImageField)
-        super().__init__(*args, **kwargs)
+        super().__init__(**kwargs)
 
     def to_internal_value(self, data):
         # Image validation is a bit grungy, so we'll just outright
@@ -1593,8 +1593,8 @@ def to_internal_value(self, data):
 # Composite field types...
 
 class _UnvalidatedField(Field):
-    def __init__(self, *args, **kwargs):
-        super().__init__(*args, **kwargs)
+    def __init__(self, **kwargs):
+        super().__init__(**kwargs)
         self.allow_blank = True
         self.allow_null = True
 
@@ -1615,7 +1615,7 @@ class ListField(Field):
         'max_length': _('Ensure this field has no more than {max_length} elements.')
     }
 
-    def __init__(self, *args, **kwargs):
+    def __init__(self, **kwargs):
         self.child = kwargs.pop('child', copy.deepcopy(self.child))
         self.allow_empty = kwargs.pop('allow_empty', True)
         self.max_length = kwargs.pop('max_length', None)
@@ -1627,7 +1627,7 @@ def __init__(self, *args, **kwargs):
             "Remove `source=` from the field declaration."
         )
 
-        super().__init__(*args, **kwargs)
+        super().__init__(**kwargs)
         self.child.bind(field_name='', parent=self)
         if self.max_length is not None:
             message = lazy_format(self.error_messages['max_length'], max_length=self.max_length)
@@ -1692,7 +1692,7 @@ class DictField(Field):
         'empty': _('This dictionary may not be empty.'),
     }
 
-    def __init__(self, *args, **kwargs):
+    def __init__(self, **kwargs):
         self.child = kwargs.pop('child', copy.deepcopy(self.child))
         self.allow_empty = kwargs.pop('allow_empty', True)
 
@@ -1702,7 +1702,7 @@ def __init__(self, *args, **kwargs):
             "Remove `source=` from the field declaration."
         )
 
-        super().__init__(*args, **kwargs)
+        super().__init__(**kwargs)
         self.child.bind(field_name='', parent=self)
 
     def get_value(self, dictionary):
@@ -1751,8 +1751,8 @@ def run_child_validation(self, data):
 class HStoreField(DictField):
     child = CharField(allow_blank=True, allow_null=True)
 
-    def __init__(self, *args, **kwargs):
-        super().__init__(*args, **kwargs)
+    def __init__(self, **kwargs):
+        super().__init__(**kwargs)
         assert isinstance(self.child, CharField), (
             "The `child` argument must be an instance of `CharField`, "
             "as the hstore extension stores values as strings."
@@ -1767,11 +1767,11 @@ class JSONField(Field):
     # Workaround for isinstance calls when importing the field isn't possible
     _is_jsonfield = True
 
-    def __init__(self, *args, **kwargs):
+    def __init__(self, **kwargs):
         self.binary = kwargs.pop('binary', False)
         self.encoder = kwargs.pop('encoder', None)
         self.decoder = kwargs.pop('decoder', None)
-        super().__init__(*args, **kwargs)
+        super().__init__(**kwargs)
 
     def get_value(self, dictionary):
         if html.is_html_input(dictionary) and self.field_name in dictionary:

tests/test_fields.py

@@ -1986,6 +1986,11 @@ def test_collection_types_are_invalid_input(self):
             field.to_internal_value(input_value)
         assert exc_info.value.detail == ['Expected a list of items but got type "dict".']
 
+    def test_constructor_misuse_raises(self):
+        # Test that `ListField` can only be instantiated with keyword arguments
+        with pytest.raises(TypeError):
+            serializers.ListField(serializers.CharField())
+
 
 class TestNestedListField(FieldValues):
     """