Allow type checkers to make serializers generic (#7385)

rest_framework/serializers.py

@@ -121,6 +121,10 @@ class BaseSerializer(Field):
             return cls.many_init(*args, **kwargs)
         return super().__new__(cls, *args, **kwargs)
 
+    # Allow type checkers to make serializers generic.
+    def __class_getitem__(cls, *args, **kwargs):
+        return cls
+
     @classmethod
     def many_init(cls, *args, **kwargs):
         """

tests/test_serializer.py

@@ -1,6 +1,7 @@
 import inspect
 import pickle
 import re
+import sys
 from collections import ChainMap
 from collections.abc import Mapping
 
@@ -204,6 +205,13 @@ class TestSerializer:
                 exceptions.ErrorDetail(string='Raised error', code='invalid')
             ]}
 
+    @pytest.mark.skipif(
+        sys.version_info < (3, 7),
+        reason="subscriptable classes requires Python 3.7 or higher",
+    )
+    def test_serializer_is_subscriptable(self):
+        assert serializers.Serializer is serializers.Serializer["foo"]
+
 
 class TestValidateMethod:
     def test_non_field_error_validate_method(self):

tests/test_serializer_lists.py

@@ -1,3 +1,5 @@
+import sys
+
 import pytest
 from django.http import QueryDict
 from django.utils.datastructures import MultiValueDict
@@ -55,6 +57,13 @@ class TestListSerializer:
         assert serializer.is_valid()
         assert serializer.validated_data == expected_output
 
+    @pytest.mark.skipif(
+        sys.version_info < (3, 7),
+        reason="subscriptable classes requires Python 3.7 or higher",
+    )
+    def test_list_serializer_is_subscriptable(self):
+        assert serializers.ListSerializer is serializers.ListSerializer["foo"]
+
 
 class TestListSerializerContainingNestedSerializer:
     """