bpo-43682: @staticmethod inherits method attributes

Static methods (@staticmethod) and class methods (@classmethod) now inherit the method attributes (__module__, __name__, __qualname__, __doc__, __annotations__) and have a new __wrapped__ attribute. Changes: * Add a repr() method to staticmethod and classmethod types. * Add tests on the @classmethod decorator.
python · vstinner · Apr 9, 2021 · Apr 7, 2021 · Apr 7, 2021 · Apr 8, 2021
commit b50eb0714a1f5836e1d881067d6ca72c628c8100
diff --git a/Doc/library/functions.rst b/Doc/library/functions.rst
@@ -269,6 +269,11 @@ are always available.  They are listed here in alphabetical order.
       Class methods can now wrap other :term:`descriptors <descriptor>` such as
       :func:`property`.
 
+   .. versionchanged:: 3.10
+      Class methods now inherit the method attributes (``__module__``,
+      ``__name__``, ``__qualname__``, ``__doc__`` and ``__annotations__``) and
+      have a new ``__wrapped__`` attribute.
+
 .. function:: compile(source, filename, mode, flags=0, dont_inherit=False, optimize=-1)
 
    Compile the *source* into a code or AST object.  Code objects can be executed
@@ -1632,6 +1637,11 @@ are always available.  They are listed here in alphabetical order.
 
    For more information on static methods, see :ref:`types`.
 
+   .. versionchanged:: 3.10
+      Static methods now inherit the method attributes (``__module__``,
+      ``__name__``, ``__qualname__``, ``__doc__`` and ``__annotations__``) and
+      have a new ``__wrapped__`` attribute.
+
 
 .. index::
    single: string; str() (built-in function)

diff --git a/Doc/whatsnew/3.10.rst b/Doc/whatsnew/3.10.rst
@@ -617,6 +617,12 @@ Other Language Changes
   respectively.
   (Contributed by Joshua Bronson, Daniel Pope, and Justin Wang in :issue:`31861`.)
 
+* Static methods (:func:`@staticmethod <staticmethod>`) and class methods
+  (:func:`@classmethod <classmethod>`) now inherit the method attributes
+  (``__module__``, ``__name__``, ``__qualname__``, ``__doc__``,
+  ``__annotations__``) and have a new ``__wrapped__`` attribute.
+  (Contributed by Victor Stinner in :issue:`43682`.)
+
 
 New Modules
 ===========

diff --git a/Lib/test/test_decorators.py b/Lib/test/test_decorators.py
@@ -1,3 +1,4 @@
+from test import support
 import unittest
 
 def funcattrs(**kwds):
@@ -76,11 +77,39 @@ def foo(): return 42
         self.assertEqual(C.foo(), 42)
         self.assertEqual(C().foo(), 42)
 
-    def test_staticmethod_function(self):
-        @staticmethod
-        def notamethod(x):
+    def check_wrapper_attrs(self, wrapper, func):
+        self.assertIs(wrapper.__wrapped__, func)
+
+        for attr in ('__module__', '__qualname__', '__name__',
+                     '__doc__', '__annotations__'):
+            self.assertIs(getattr(wrapper, attr),
+                          getattr(func, attr))
+
+    def test_staticmethod(self):
+        def func(x):
+            return x
+        wrapper = staticmethod(func)
+
+        self.assertIs(wrapper.__func__, func)
+        self.check_wrapper_attrs(wrapper, func)
+
+        self.assertEqual(repr(wrapper),
+                         f'<staticmethod({func!r})>')
+
+        self.assertRaises(TypeError, wrapper, 1)
+
+    def test_classmethod(self):
+        def func(x):
             return x
-        self.assertRaises(TypeError, notamethod, 1)
+        wrapper = classmethod(func)
+
+        self.assertIs(wrapper.__func__, func)
+        self.check_wrapper_attrs(wrapper, func)
+
+        self.assertEqual(repr(wrapper),
+                         f'<classmethod({func!r})>')
+
+        self.assertRaises(TypeError, wrapper, 1)
 
     def test_dotted(self):
         decorators = MiscDecorators()

diff --git a/Misc/NEWS.d/next/Core and Builtins/2021-04-08-01-06-22.bpo-43682.eUn4p5.rst b/Misc/NEWS.d/next/Core and Builtins/2021-04-08-01-06-22.bpo-43682.eUn4p5.rst
@@ -0,0 +1,5 @@
+Static methods (:func:`@staticmethod <staticmethod>`) and class methods
+(:func:`@classmethod <classmethod>`) now inherit the method attributes
+(``__module__``, ``__name__``, ``__qualname__``, ``__doc__``,
+``__annotations__``) and have a new ``__wrapped__`` attribute.
+Patch by Victor Stinner.
diff --git a/Objects/funcobject.c b/Objects/funcobject.c
@@ -639,7 +639,7 @@ static PyObject*
 func_repr(PyFunctionObject *op)
 {
     return PyUnicode_FromFormat("<function %U at %p>",
-                               op->func_qualname, op);
+                                op->func_qualname, op);
 }
 
 static int
@@ -715,6 +715,50 @@ PyTypeObject PyFunction_Type = {
 };
 
 
+static int
+functools_copy_attr(PyObject *wrapper, PyObject *wrapped, PyObject *name)
+{
+    PyObject *value = PyObject_GetAttr(wrapped, name);
+    if (value == NULL) {
+        if (PyErr_ExceptionMatches(PyExc_AttributeError)) {
+            PyErr_Clear();
+            return 0;
+        }
+        return -1;
+    }
+
+    int res = PyObject_SetAttr(wrapper, name, value);
+    Py_DECREF(value);
+    return res;
+}
+
+// Similar to functools.wraps(wrapper, wrapped)
+static int
+functools_wraps(PyObject *wrapper, PyObject *wrapped)
+{
+#define COPY_ATTR(ATTR) \
+    do { \
+        _Py_IDENTIFIER(ATTR); \
+        PyObject *attr = _PyUnicode_FromId(&PyId_ ## ATTR); \
+        if (attr == NULL) { \
+            return -1; \
+        } \
+        if (functools_copy_attr(wrapper, wrapped, attr) < 0) { \
+            return -1; \
+        } \
+    } while (0) \
+
+    COPY_ATTR(__module__);
+    COPY_ATTR(__name__);
+    COPY_ATTR(__qualname__);
+    COPY_ATTR(__doc__);
+    COPY_ATTR(__annotations__);
+    return 0;
+
+#undef COPY_ATTR
+}
+
+
 /* Class method object */
 
 /* A class method receives the class as implicit first argument,
@@ -798,11 +842,16 @@ cm_init(PyObject *self, PyObject *args, PyObject *kwds)
         return -1;
     Py_INCREF(callable);
     Py_XSETREF(cm->cm_callable, callable);
+
+    if (functools_wraps((PyObject *)cm, cm->cm_callable) < 0) {
+        return -1;
+    }
     return 0;
 }
 
 static PyMemberDef cm_memberlist[] = {
     {"__func__", T_OBJECT, offsetof(classmethod, cm_callable), READONLY},
+    {"__wrapped__", T_OBJECT, offsetof(classmethod, cm_callable), READONLY},
     {NULL}  /* Sentinel */
 };
 
@@ -821,13 +870,17 @@ cm_get___isabstractmethod__(classmethod *cm, void *closure)
 
 static PyGetSetDef cm_getsetlist[] = {
     {"__isabstractmethod__",
-     (getter)cm_get___isabstractmethod__, NULL,
-     NULL,
-     NULL},
+     (getter)cm_get___isabstractmethod__, NULL, NULL, NULL},
     {"__dict__", PyObject_GenericGetDict, PyObject_GenericSetDict, NULL, NULL},
     {NULL} /* Sentinel */
 };
 
+static PyObject*
+cm_repr(classmethod *cm)
+{
+    return PyUnicode_FromFormat("<classmethod(%R)>", cm->cm_callable);
+}
+
 PyDoc_STRVAR(classmethod_doc,
 "classmethod(function) -> method\n\
 \n\
@@ -860,7 +913,7 @@ PyTypeObject PyClassMethod_Type = {
     0,                                          /* tp_getattr */
     0,                                          /* tp_setattr */
     0,                                          /* tp_as_async */
-    0,                                          /* tp_repr */
+    (reprfunc)cm_repr,                          /* tp_repr */
     0,                                          /* tp_as_number */
     0,                                          /* tp_as_sequence */
     0,                                          /* tp_as_mapping */
@@ -980,11 +1033,16 @@ sm_init(PyObject *self, PyObject *args, PyObject *kwds)
         return -1;
     Py_INCREF(callable);
     Py_XSETREF(sm->sm_callable, callable);
+
+    if (functools_wraps((PyObject *)sm, sm->sm_callable) < 0) {
+        return -1;
+    }
     return 0;
 }
 
 static PyMemberDef sm_memberlist[] = {
     {"__func__", T_OBJECT, offsetof(staticmethod, sm_callable), READONLY},
+    {"__wrapped__", T_OBJECT, offsetof(staticmethod, sm_callable), READONLY},
     {NULL}  /* Sentinel */
 };
 
@@ -1003,13 +1061,17 @@ sm_get___isabstractmethod__(staticmethod *sm, void *closure)
 
 static PyGetSetDef sm_getsetlist[] = {
     {"__isabstractmethod__",
-     (getter)sm_get___isabstractmethod__, NULL,
-     NULL,
-     NULL},
+     (getter)sm_get___isabstractmethod__, NULL, NULL, NULL},
     {"__dict__", PyObject_GenericGetDict, PyObject_GenericSetDict, NULL, NULL},
     {NULL} /* Sentinel */
 };
 
+static PyObject*
+sm_repr(staticmethod *sm)
+{
+    return PyUnicode_FromFormat("<staticmethod(%R)>", sm->sm_callable);
+}
+
 PyDoc_STRVAR(staticmethod_doc,
 "staticmethod(function) -> method\n\
 \n\
@@ -1040,7 +1102,7 @@ PyTypeObject PyStaticMethod_Type = {
     0,                                          /* tp_getattr */
     0,                                          /* tp_setattr */
     0,                                          /* tp_as_async */
-    0,                                          /* tp_repr */
+    (reprfunc)sm_repr,                          /* tp_repr */
     0,                                          /* tp_as_number */
     0,                                          /* tp_as_sequence */
     0,                                          /* tp_as_mapping */