Allow generic requests, responses, fields, views (#8825)

Allow Request, Response, Field, and GenericAPIView to be subscriptable.
This allows the classes to be made generic for type checking.

This is especially useful since monkey patching DRF can be problematic
as seen in this [issue][1].

[1]: typeddjango/djangorestframework-stubs#299

Author: jalaziz

rest_framework/fields.py

@@ -356,6 +356,10 @@ def __init__(self, *, read_only=False, write_only=False,
         messages.update(error_messages or {})
         self.error_messages = messages
 
+    # Allow generic typing checking for fields.
+    def __class_getitem__(cls, *args, **kwargs):
+        return cls
+
     def bind(self, field_name, parent):
         """
         Initializes the field name and parent for the field instance.

rest_framework/generics.py

@@ -45,6 +45,10 @@ class GenericAPIView(views.APIView):
     # The style to use for queryset pagination.
     pagination_class = api_settings.DEFAULT_PAGINATION_CLASS
 
+    # Allow generic typing checking for generic views.
+    def __class_getitem__(cls, *args, **kwargs):
+        return cls
+
     def get_queryset(self):
         """
         Get the list of items for this view.

rest_framework/request.py

@@ -186,6 +186,10 @@ def __repr__(self):
             self.method,
             self.get_full_path())
 
+    # Allow generic typing checking for requests.
+    def __class_getitem__(cls, *args, **kwargs):
+        return cls
+
     def _default_negotiator(self):
         return api_settings.DEFAULT_CONTENT_NEGOTIATION_CLASS()
 

rest_framework/response.py

@@ -46,6 +46,10 @@ def __init__(self, data=None, status=None,
             for name, value in headers.items():
                 self[name] = value
 
+    # Allow generic typing checking for responses.
+    def __class_getitem__(cls, *args, **kwargs):
+        return cls
+
     @property
     def rendered_content(self):
         renderer = getattr(self, 'accepted_renderer', None)

tests/test_fields.py

@@ -2,6 +2,7 @@
 import math
 import os
 import re
+import sys
 import uuid
 from decimal import ROUND_DOWN, ROUND_UP, Decimal
 
@@ -625,6 +626,15 @@ def test_parent_binding(self):
         assert field.root is parent
 
 
+class TestTyping(TestCase):
+    @pytest.mark.skipif(
+        sys.version_info < (3, 7),
+        reason="subscriptable classes requires Python 3.7 or higher",
+    )
+    def test_field_is_subscriptable(self):
+        assert serializers.Field is serializers.Field["foo"]
+
+
 # Tests for field input and output values.
 # ----------------------------------------
 

tests/test_generics.py

@@ -1,3 +1,5 @@
+import sys
+
 import pytest
 from django.db import models
 from django.http import Http404
@@ -698,3 +700,26 @@ def list(self, request):
         serializer = response.serializer
 
         assert serializer.context is context
+
+
+class TestTyping(TestCase):
+    @pytest.mark.skipif(
+        sys.version_info < (3, 7),
+        reason="subscriptable classes requires Python 3.7 or higher",
+    )
+    def test_genericview_is_subscriptable(self):
+        assert generics.GenericAPIView is generics.GenericAPIView["foo"]
+
+    @pytest.mark.skipif(
+        sys.version_info < (3, 7),
+        reason="subscriptable classes requires Python 3.7 or higher",
+    )
+    def test_listview_is_subscriptable(self):
+        assert generics.ListAPIView is generics.ListAPIView["foo"]
+
+    @pytest.mark.skipif(
+        sys.version_info < (3, 7),
+        reason="subscriptable classes requires Python 3.7 or higher",
+    )
+    def test_instanceview_is_subscriptable(self):
+        assert generics.RetrieveAPIView is generics.RetrieveAPIView["foo"]

tests/test_request.py

@@ -3,6 +3,7 @@
 """
 import copy
 import os.path
+import sys
 import tempfile
 
 import pytest
@@ -352,3 +353,12 @@ class TestDeepcopy(TestCase):
     def test_deepcopy_works(self):
         request = Request(factory.get('/', secure=False))
         copy.deepcopy(request)
+
+
+class TestTyping(TestCase):
+    @pytest.mark.skipif(
+        sys.version_info < (3, 7),
+        reason="subscriptable classes requires Python 3.7 or higher",
+    )
+    def test_request_is_subscriptable(self):
+        assert Request is Request["foo"]

tests/test_response.py

@@ -1,3 +1,6 @@
+import sys
+
+import pytest
 from django.test import TestCase, override_settings
 from django.urls import include, path, re_path
 
@@ -283,3 +286,12 @@ def test_form_has_label_and_help_text(self):
         self.assertEqual(resp['Content-Type'], 'text/html; charset=utf-8')
         # self.assertContains(resp, 'Text comes here')
         # self.assertContains(resp, 'Text description.')
+
+
+class TestTyping(TestCase):
+    @pytest.mark.skipif(
+        sys.version_info < (3, 7),
+        reason="subscriptable classes requires Python 3.7 or higher",
+    )
+    def test_response_is_subscriptable(self):
+        assert Response is Response["foo"]