Use dict and set literals instead of calls to dict() and set() (#5559)

Set literals are available on all supported Python versions. They are
idiomatic and always faster:

$ python3 -m timeit '{}'
10000000 loops, best of 3: 0.0357 usec per loop
$ python3 -m timeit 'dict()'
10000000 loops, best of 3: 0.104 usec per loop

$ python3 -m timeit '{1, 2, 3}'
10000000 loops, best of 3: 0.0754 usec per loop
$ python3 -m timeit 'set([1, 2, 3])'
1000000 loops, best of 3: 0.228 usec per loop

rest_framework/decorators.py

@@ -46,7 +46,7 @@ def api_view(http_method_names=None, exclude_from_schema=False):
         assert isinstance(http_method_names, (list, tuple)), \
             '@api_view expected a list of strings, received %s' % type(http_method_names).__name__
 
-        allowed_methods = set(http_method_names) | set(('options',))
+        allowed_methods = set(http_method_names) | {'options'}
         WrappedAPIView.http_method_names = [method.lower() for method in allowed_methods]
 
         def handler(self, *args, **kwargs):

rest_framework/schemas/generators.py

@@ -118,9 +118,9 @@ def distribute_links(obj):
 
 
 def is_custom_action(action):
-    return action not in set([
+    return action not in {
         'retrieve', 'list', 'create', 'update', 'partial_update', 'destroy'
-    ])
+    }
 
 
 def endpoint_ordering(endpoint):

rest_framework/schemas/inspectors.py

@@ -385,11 +385,11 @@ class AutoSchema(ViewInspector):
         view = self.view
 
         # Core API supports the following request encodings over HTTP...
-        supported_media_types = set((
+        supported_media_types = {
             'application/json',
             'application/x-www-form-urlencoded',
             'multipart/form-data',
-        ))
+        }
         parser_classes = getattr(view, 'parser_classes', [])
         for parser_class in parser_classes:
             media_type = getattr(parser_class, 'media_type', None)

rest_framework/serializers.py

@@ -1172,13 +1172,13 @@ class ModelSerializer(Serializer):
             # Some model fields may introduce kwargs that would not be valid
             # for the choice field. We need to strip these out.
             # Eg. models.DecimalField(max_digits=3, decimal_places=1, choices=DECIMAL_CHOICES)
-            valid_kwargs = set((
+            valid_kwargs = {
                 'read_only', 'write_only',
                 'required', 'default', 'initial', 'source',
                 'label', 'help_text', 'style',
                 'error_messages', 'validators', 'allow_null', 'allow_blank',
                 'choices'
-            ))
+            }
             for key in list(field_kwargs.keys()):
                 if key not in valid_kwargs:
                     field_kwargs.pop(key)

tests/test_fields.py

@@ -1618,15 +1618,15 @@ class TestMultipleChoiceField(FieldValues):
     """
     valid_inputs = {
         (): set(),
-        ('aircon',): set(['aircon']),
-        ('aircon', 'manual'): set(['aircon', 'manual']),
+        ('aircon',): {'aircon'},
+        ('aircon', 'manual'): {'aircon', 'manual'},
     }
     invalid_inputs = {
         'abc': ['Expected a list of items but got type "str".'],
         ('aircon', 'incorrect'): ['"incorrect" is not a valid choice.']
     }
     outputs = [
-        (['aircon', 'manual', 'incorrect'], set(['aircon', 'manual', 'incorrect']))
+        (['aircon', 'manual', 'incorrect'], {'aircon', 'manual', 'incorrect'})
     ]
     field = serializers.MultipleChoiceField(
         choices=[

tests/test_multitable_inheritance.py

@@ -44,7 +44,7 @@ class InheritedModelSerializationTests(TestCase):
         """
         child = ChildModel(name1='parent name', name2='child name')
         serializer = DerivedModelSerializer(child)
-        assert set(serializer.data.keys()) == set(['name1', 'name2', 'id'])
+        assert set(serializer.data.keys()) == {'name1', 'name2', 'id'}
 
     def test_onetoone_primary_key_model_fields_as_expected(self):
         """
@@ -54,7 +54,7 @@ class InheritedModelSerializationTests(TestCase):
         parent = ParentModel.objects.create(name1='parent name')
         associate = AssociatedModel.objects.create(name='hello', ref=parent)
         serializer = AssociatedModelSerializer(associate)
-        assert set(serializer.data.keys()) == set(['name', 'ref'])
+        assert set(serializer.data.keys()) == {'name', 'ref'}
 
     def test_data_is_valid_without_parent_ptr(self):
         """

tests/test_one_to_one_with_inheritance.py

@@ -41,4 +41,4 @@ class InheritedModelSerializationTests(TestCase):
         child = ChildModel(name1='parent name', name2='child name')
         serializer = DerivedModelSerializer(child)
         self.assertEqual(set(serializer.data.keys()),
-                         set(['name1', 'name2', 'id', 'childassociatedmodel']))
+                         {'name1', 'name2', 'id', 'childassociatedmodel'})

tests/test_renderers.py

@@ -316,7 +316,7 @@ class JSONRendererTests(TestCase):
     def test_render_dict_abc_obj(self):
         class Dict(MutableMapping):
             def __init__(self):
-                self._dict = dict()
+                self._dict = {}
 
             def __getitem__(self, key):
                 return self._dict.__getitem__(key)

tests/test_serializer_nested.py

@@ -194,11 +194,11 @@ class TestNestedSerializerWithList:
         serializer = self.Serializer(data=input_data)
 
         assert serializer.is_valid()
-        assert serializer.validated_data['nested']['example'] == set([1, 2])
+        assert serializer.validated_data['nested']['example'] == {1, 2}
 
     def test_nested_serializer_with_list_multipart(self):
         input_data = QueryDict('nested.example=1&nested.example=2')
         serializer = self.Serializer(data=input_data)
 
         assert serializer.is_valid()
-        assert serializer.validated_data['nested']['example'] == set([1, 2])
+        assert serializer.validated_data['nested']['example'] == {1, 2}