pablogsal · Jan 20, 2021 · Jan 20, 2021 · Jan 20, 2021 · Jan 20, 2021 · Jan 20, 2021
diff --git a/Lib/test/test_call.py b/Lib/test/test_call.py
@@ -713,5 +713,66 @@ def test_multiple_values(self):
             A().method_two_args("x", "y", x="oops")
 
 
+class NoSelfClass:
+    def foo():
+        pass
+
+    def foo1(x, y):
+        pass
+
+    def foo2(self, y):
+        pass
+
+    @classmethod
+    def clsmethod(x, y):
+        pass
+
+    @staticmethod
+    def stmethod(x, y):
+        pass
+
+
+@cpython_only
+class TestErrorMessagesInMethodsGiveHintAboutSelf(unittest.TestCase):
+    @contextlib.contextmanager
+    def check_raises_type_error(self, message):
+        with self.assertRaises(TypeError) as cm:
+            yield
+        self.assertEqual(str(cm.exception), message)
+
+
+    def test_method_with_missing_self_no_args(self):
+
+        msg = ("NoSelfClass.foo() takes 0 positional arguments but 1 was given. "
+               "Did you forget 'self' in the method definition?")
+        with self.check_raises_type_error(msg):
+            NoSelfClass().foo()
+
+    def test_method_with_missing_self_args(self):
+
+        msg = ("NoSelfClass.foo1() takes 2 positional arguments but 3 were given. "
+               "Did you forget 'self' in the method definition?")
+        with self.check_raises_type_error(msg):
+            NoSelfClass().foo1(1, 2)
+
+    def test_method_with_self_args(self):
+
+        msg = "NoSelfClass.foo2() takes 2 positional arguments but 3 were given"
+        with self.check_raises_type_error(msg):
+            NoSelfClass().foo2(1, 2)
+
+    def test_method_with_classmethod(self):
+
+        msg = "NoSelfClass.clsmethod() takes 2 positional arguments but 3 were given"
+        with self.check_raises_type_error(msg):
+            NoSelfClass().clsmethod(1, 2)
+
+    def test_method_with_staticmethod(self):
+
+        msg = "NoSelfClass.stmethod() takes 2 positional arguments but 3 were given"
+        with self.check_raises_type_error(msg):
+            NoSelfClass().stmethod(1, 2, 3)
+
+
 if __name__ == "__main__":
     unittest.main()
diff --git a/Python/ceval.c b/Python/ceval.c
@@ -86,6 +86,7 @@ static PyObject * special_lookup(PyThreadState *, PyObject *, _Py_Identifier *);
 static int check_args_iterable(PyThreadState *, PyObject *func, PyObject *vararg);
 static void format_kwargs_error(PyThreadState *, PyObject *func, PyObject *kwargs);
 static void format_awaitable_error(PyThreadState *, PyTypeObject *, int, int);
+static void improve_missing_self_error(PyThreadState* tstate, PyCodeObject* co);
 
 #define NAME_ERROR_MSG \
     "name '%.200s' is not defined"
@@ -3786,13 +3787,22 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, PyFrameObject *f, int throwflag)
                   We'll be passing `oparg + 1` to call_function, to
                   make it accept the `self` as a first argument.
                 */
+
+                PyObject **pfunc = (*(&sp)) - (oparg + 1) - 1;
+                PyObject *func = *pfunc;
+                PyCodeObject *co = (PyCodeObject *)PyFunction_GET_CODE(func);
                 res = call_function(tstate, &bounds, &sp, oparg + 1, NULL);
+                if (res == NULL && oparg == co->co_argcount &&
+                    PyErr_ExceptionMatches(PyExc_TypeError)) {
+                    improve_missing_self_error(tstate, co);
+                }
                 stack_pointer = sp;
             }
 
             PUSH(res);
-            if (res == NULL)
+            if (res == NULL) {
                 goto error;
+            }
             DISPATCH();
         }
 
@@ -5998,3 +6008,34 @@ void Py_LeaveRecursiveCall(void)
 {
     _Py_LeaveRecursiveCall_inline();
 }
+
+static void
+improve_missing_self_error(PyThreadState* tstate, PyCodeObject* co)
+{
+
+    PyObject *type, *val, *tb;
+    _PyErr_Fetch(tstate, &type, &val, &tb);
+
+    if (!PyUnicode_CheckExact(val)) {
+        goto exit;
+    }
+
+    if (co->co_argcount > 0 && co->co_varnames && PyTuple_GET_SIZE(co->co_varnames) > 0) {
+        PyObject* first_arg = PyTuple_GET_ITEM(co->co_varnames, 0);
+        if (_PyUnicode_EqualToASCIIString(first_arg, "self")) {
+            PyErr_Clear();
+            goto exit;
+        }
+    }
+
+    PyObject* new_val = PyUnicode_FromFormat("%U. Did you forget 'self' in the method"
+                                             " definition?", val);
+    if (new_val == NULL) {
+        PyErr_Clear();
+        goto exit;
+    }
+    Py_DECREF(val);
+    val = new_val;
+exit:
+    PyErr_Restore(type, val, tb);
+}