gh-82012: Deprecate bitwise inversion (~) of bool

timhoffm · timhoffm · commit dbf50e8148e8 · 2023-04-12T21:49:30.000+02:00
The bitwise inversion operator on bool returns the bitwise inversion of the underlying int value; i.e. `~True == -2` such that `bool(~True) == True`. It's a common pitfall that users mistake `~` as negation operator and actually want `not`. Supporting `~` is an artifact of bool inheriting from int. Since there is no real use-case for the current behavior, let's deprecate `~` on bool and later raise an error. This removes a potential source errors for users. Full reasoning: #82012 (comment)
diff --git a/Lib/test/test_bool.py b/Lib/test/test_bool.py
@@ -58,8 +58,10 @@ def test_math(self):
         self.assertEqual(-True, -1)
         self.assertEqual(abs(True), 1)
         self.assertIsNot(abs(True), True)
-        self.assertEqual(~False, -1)
-        self.assertEqual(~True, -2)
+        with self.assertWarns(DeprecationWarning):
+            self.assertEqual(~False, -1)
+        with self.assertWarns(DeprecationWarning):
+            self.assertEqual(~True, -2)
 
         self.assertEqual(False+2, 2)
         self.assertEqual(True+2, 3)
diff --git a/Objects/boolobject.c b/Objects/boolobject.c
@@ -73,6 +73,22 @@ bool_vectorcall(PyObject *type, PyObject * const*args,
 
 /* Arithmetic operations redefined to return bool if both args are bool. */
 
+static PyObject *
+bool_invert(PyObject *v)
+{
+    if (PyErr_WarnEx(PyExc_DeprecationWarning,
+                     "Bitwise inversion '~' on bool is deprecated. This "
+                     "returns the bitwise inversion of the underlying int "
+                     "object and is usually not what you expect from negating "
+                     "a bool. Use the 'not' operator for boolean negation or "
+                     "~int(x) if you really want the bitwise inversion of the "
+                     "underlying int.",
+                     1) < 0) {
+        return NULL;
+    }
+    return PyLong_Type.tp_as_number->nb_invert(v);
+}
+
 static PyObject *
 bool_and(PyObject *a, PyObject *b)
 {
@@ -119,7 +135,7 @@ static PyNumberMethods bool_as_number = {
     0,                          /* nb_positive */
     0,                          /* nb_absolute */
     0,                          /* nb_bool */
-    0,                          /* nb_invert */
+    (unaryfunc)bool_invert,     /* nb_invert */
     0,                          /* nb_lshift */
     0,                          /* nb_rshift */
     bool_and,                   /* nb_and */
