pythongh-104600: Make type.__type_params__ writable

JelleZijlstra · May 18, 2023 · 41b9279 · 41b9279
1 parent 94c8eda
commit 41b9279
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Showing 2 changed files with 50 additions and 7 deletions.
diff --git a/Lib/test/test_builtin.py b/Lib/test/test_builtin.py
@@ -18,6 +18,7 @@
 import sys
 import traceback
 import types
+import typing
 import unittest
 import warnings
 from contextlib import ExitStack
@@ -2485,6 +2486,18 @@ def test_type_qualname(self):
             A.__qualname__ = b'B'
         self.assertEqual(A.__qualname__, 'D.E')
 
+    def test_type_typeparams(self):
+        class A[T]:
+            pass
+        T, = A.__type_params__
+        self.assertIsInstance(T, typing.TypeVar)
+        A.__type_params__ = "whatever"
+        self.assertEqual(A.__type_params__, "whatever")
+        del A.__type_params__
+        self.assertEqual(A.__type_params__, ())
+        with self.assertRaises(AttributeError):
+            del A.__type_params__
+
     def test_type_doc(self):
         for doc in 'x', '\xc4', '\U0001f40d', 'x\x00y', b'x', 42, None:
             A = type('A', (), {'__doc__': doc})

diff --git a/Objects/typeobject.c b/Objects/typeobject.c
@@ -1460,6 +1460,36 @@ type_get_annotations(PyTypeObject *type, void *context)
     return annotations;
 }
 
+static int
+type_set_annotations(PyTypeObject *type, PyObject *value, void *context)
+{
+    if (_PyType_HasFeature(type, Py_TPFLAGS_IMMUTABLETYPE)) {
+        PyErr_Format(PyExc_TypeError,
+                     "cannot set '__annotations__' attribute of immutable type '%s'",
+                     type->tp_name);
+        return -1;
+    }
+
+    int result;
+    PyObject *dict = lookup_tp_dict(type);
+    if (value != NULL) {
+        /* set */
+        result = PyDict_SetItem(dict, &_Py_ID(__annotations__), value);
+    } else {
+        /* delete */
+        if (!PyDict_Contains(dict, &_Py_ID(__annotations__))) {
+            PyErr_Format(PyExc_AttributeError, "__annotations__");
+            return -1;
+        }
+        result = PyDict_DelItem(dict, &_Py_ID(__annotations__));
+    }
+
+    if (result == 0) {
+        PyType_Modified(type);
+    }
+    return result;
+}
+
 static PyObject *
 type_get_type_params(PyTypeObject *type, void *context)
 {
@@ -1473,11 +1503,11 @@ type_get_type_params(PyTypeObject *type, void *context)
 }
 
 static int
-type_set_annotations(PyTypeObject *type, PyObject *value, void *context)
+type_set_type_params(PyTypeObject *type, PyObject *value, void *context)
 {
     if (_PyType_HasFeature(type, Py_TPFLAGS_IMMUTABLETYPE)) {
         PyErr_Format(PyExc_TypeError,
-                     "cannot set '__annotations__' attribute of immutable type '%s'",
+                     "cannot set '__type_params__' attribute of immutable type '%s'",
                      type->tp_name);
         return -1;
     }
@@ -1486,14 +1516,14 @@ type_set_annotations(PyTypeObject *type, PyObject *value, void *context)
     PyObject *dict = lookup_tp_dict(type);
     if (value != NULL) {
         /* set */
-        result = PyDict_SetItem(dict, &_Py_ID(__annotations__), value);
+        result = PyDict_SetItem(dict, &_Py_ID(__type_params__), value);
     } else {
         /* delete */
-        if (!PyDict_Contains(dict, &_Py_ID(__annotations__))) {
-            PyErr_Format(PyExc_AttributeError, "__annotations__");
+        if (!PyDict_Contains(dict, &_Py_ID(__type_params__))) {
+            PyErr_Format(PyExc_AttributeError, "__type_params__");
             return -1;
         }
-        result = PyDict_DelItem(dict, &_Py_ID(__annotations__));
+        result = PyDict_DelItem(dict, &_Py_ID(__type_params__));
     }
 
     if (result == 0) {
@@ -1548,7 +1578,7 @@ static PyGetSetDef type_getsets[] = {
     {"__doc__", (getter)type_get_doc, (setter)type_set_doc, NULL},
     {"__text_signature__", (getter)type_get_text_signature, NULL, NULL},
     {"__annotations__", (getter)type_get_annotations, (setter)type_set_annotations, NULL},
-    {"__type_params__", (getter)type_get_type_params, NULL, NULL},
+    {"__type_params__", (getter)type_get_type_params, (setter)type_set_type_params, NULL},
     {0}
 };