Support GenericAliases for Python 3.9+ (#553)

.github/workflows/ci.yml

@@ -23,10 +23,10 @@ jobs:
     steps:
     - name: Checkout
       uses: actions/checkout@v2
-    - name: Setup Python 3.8
+    - name: Setup Python 3.9
       uses: actions/setup-python@v2
       with:
-        python-version: 3.8
+        python-version: 3.9
     - name: Cache PyPI
       uses: actions/cache@v2
       with:

CHANGES/553.feature

@@ -0,0 +1 @@
+Support ``GenericAliases`` (``MultiDict[str]``) for Python 3.9+

multidict/_abc.py

@@ -1,4 +1,6 @@
 import abc
+import sys
+import types
 from collections.abc import Mapping, MutableMapping
 
 
@@ -7,8 +9,15 @@ class _TypingMeta(abc.ABCMeta):
     # basically MultiMapping[str] and other generic-like type instantiations
     # are emulated.
     # Note: real type hints are provided by __init__.pyi stub file
-    def __getitem__(self, key):
-        return self
+    if sys.version_info >= (3, 9):
+
+        def __getitem__(self, key):
+            return types.GenericAlias(self, key)
+
+    else:
+
+        def __getitem__(self, key):
+            return self
 
 
 class MultiMapping(Mapping, metaclass=_TypingMeta):

multidict/_multidict.c

@@ -872,12 +872,17 @@ PyDoc_STRVAR(multidict_popitem_doc,
 PyDoc_STRVAR(multidict_update_doc,
 "Update the dictionary from *other*, overwriting existing keys.");
 
+
+#if PY_MAJOR_VERSION >= 3 && PY_MINOR_VERSION >= 9
+#define multidict_class_getitem Py_GenericAlias
+#else
 static inline PyObject *
 multidict_class_getitem(PyObject *self, PyObject *arg)
 {
     Py_INCREF(self);
     return self;
 }
+#endif
 
 
 PyDoc_STRVAR(sizeof__doc__,

tests/test_multidict.py

@@ -71,19 +71,6 @@ def test_proxy_copy(dict_cls, proxy_cls):
     assert d1 is not d2
 
 
-@pytest.mark.skipif(
-    sys.version_info < (3, 7),
-    reason="__class_getitem__ is supported started from Python 3.7",
-)
-@pytest.mark.parametrize(
-    "cls",
-    ["MultiDict", "CIMultiDict", "MultiDictProxy", "CIMultiDictProxy"],
-    indirect=True,
-)
-def test_class_getitem(cls):
-    assert cls[str] is cls
-
-
 @pytest.mark.parametrize(
     "cls",
     ["MultiDict", "CIMultiDict", "MultiDictProxy", "CIMultiDictProxy"],

tests/test_mypy.py

@@ -1,3 +1,8 @@
+import sys
+import types
+
+import pytest
+
 import multidict
 
 
@@ -12,3 +17,35 @@ def test_classes_not_abstract() -> None:
     d2.getall("a")
     d3.getone("a")
     d4.getall("a")
+
+
+@pytest.mark.skipif(
+    sys.version_info >= (3, 9),
+    reason="Python 3.9 GenericAlias cannot be used in isinstance()/issubclass() checks",
+)
+@pytest.mark.skipif(
+    sys.version_info < (3, 7),
+    reason="Python 3.5 and 3.6 has no __class_getitem__ method",
+)
+def test_class_getitem(_multidict) -> None:
+    assert issubclass(_multidict.MultiDict[str], _multidict.MultiDict)
+    assert issubclass(_multidict.MultiDictProxy[str], _multidict.MultiDictProxy)
+    assert issubclass(_multidict.CIMultiDict[str], _multidict.CIMultiDict)
+    assert issubclass(_multidict.CIMultiDictProxy[str], _multidict.CIMultiDictProxy)
+
+
+@pytest.mark.skipif(
+    sys.version_info < (3, 9), reason="Python 3.9 is required for GenericAlias"
+)
+def test_generic_alias(_multidict) -> None:
+
+    assert _multidict.MultiDict[int] == types.GenericAlias(_multidict.MultiDict, (int,))
+    assert _multidict.MultiDictProxy[int] == types.GenericAlias(
+        _multidict.MultiDictProxy, (int,)
+    )
+    assert _multidict.CIMultiDict[int] == types.GenericAlias(
+        _multidict.CIMultiDict, (int,)
+    )
+    assert _multidict.CIMultiDictProxy[int] == types.GenericAlias(
+        _multidict.CIMultiDictProxy, (int,)
+    )