bpo-35712: Make using NotImplemented in a boolean context issue a deprecation warning (GH-13195)
diff --git a/Doc/library/constants.rst b/Doc/library/constants.rst
index 5017159..f17e1a3 100644
--- a/Doc/library/constants.rst
+++ b/Doc/library/constants.rst
@@ -31,7 +31,7 @@
etc.) to indicate that the operation is not implemented with respect to
the other type; may be returned by the in-place binary special methods
(e.g. :meth:`__imul__`, :meth:`__iand__`, etc.) for the same purpose.
- Its truth value is true.
+ It should not be evaluated in a boolean context.
.. note::
@@ -50,6 +50,11 @@
even though they have similar names and purposes.
See :exc:`NotImplementedError` for details on when to use it.
+ .. versionchanged:: 3.9
+ Evaluating ``NotImplemented`` in a boolean context is deprecated. While
+ it currently evaluates as true, it will emit a :exc:`DeprecationWarning`.
+ It will raise a :exc:`TypeError` in a future version of Python.
+
.. index:: single: ...; ellipsis literal
.. data:: Ellipsis
diff --git a/Doc/reference/datamodel.rst b/Doc/reference/datamodel.rst
index 5b3b669..8be432d 100644
--- a/Doc/reference/datamodel.rst
+++ b/Doc/reference/datamodel.rst
@@ -156,13 +156,18 @@
object is accessed through the built-in name ``NotImplemented``. Numeric methods
and rich comparison methods should return this value if they do not implement the
operation for the operands provided. (The interpreter will then try the
- reflected operation, or some other fallback, depending on the operator.) Its
- truth value is true.
+ reflected operation, or some other fallback, depending on the operator.) It
+ should not be evaluated in a boolean context.
See
:ref:`implementing-the-arithmetic-operations`
for more details.
+ .. versionchanged:: 3.9
+ Evaluating ``NotImplemented`` in a boolean context is deprecated. While
+ it currently evaluates as true, it will emit a :exc:`DeprecationWarning`.
+ It will raise a :exc:`TypeError` in a future version of Python.
+
Ellipsis
.. index::
diff --git a/Doc/whatsnew/3.9.rst b/Doc/whatsnew/3.9.rst
index f49575d..9a8a484 100644
--- a/Doc/whatsnew/3.9.rst
+++ b/Doc/whatsnew/3.9.rst
@@ -452,6 +452,12 @@
of Python. For the majority of use cases, users can leverage the Abstract Syntax
Tree (AST) generation and compilation stage, using the :mod:`ast` module.
+* Using :data:`NotImplemented` in a boolean context has been deprecated,
+ as it is almost exclusively the result of incorrect rich comparator
+ implementations. It will be made a :exc:`TypeError` in a future version
+ of Python.
+ (Contributed by Josh Rosenberg in :issue:`35712`.)
+
* The :mod:`random` module currently accepts any hashable type as a
possible seed value. Unfortunately, some of those types are not
guaranteed to have a deterministic hash value. After Python 3.9,
diff --git a/Lib/functools.py b/Lib/functools.py
index 535fa04..e230175 100644
--- a/Lib/functools.py
+++ b/Lib/functools.py
@@ -96,6 +96,8 @@
def _le_from_lt(self, other, NotImplemented=NotImplemented):
'Return a <= b. Computed by @total_ordering from (a < b) or (a == b).'
op_result = self.__lt__(other)
+ if op_result is NotImplemented:
+ return op_result
return op_result or self == other
def _ge_from_lt(self, other, NotImplemented=NotImplemented):
@@ -136,6 +138,8 @@
def _ge_from_gt(self, other, NotImplemented=NotImplemented):
'Return a >= b. Computed by @total_ordering from (a > b) or (a == b).'
op_result = self.__gt__(other)
+ if op_result is NotImplemented:
+ return op_result
return op_result or self == other
def _le_from_gt(self, other, NotImplemented=NotImplemented):
diff --git a/Lib/ipaddress.py b/Lib/ipaddress.py
index 9c47405..7024339 100644
--- a/Lib/ipaddress.py
+++ b/Lib/ipaddress.py
@@ -1398,7 +1398,7 @@
def __eq__(self, other):
address_equal = IPv4Address.__eq__(self, other)
- if not address_equal or address_equal is NotImplemented:
+ if address_equal is NotImplemented or not address_equal:
return address_equal
try:
return self.network == other.network
@@ -2096,7 +2096,7 @@
def __eq__(self, other):
address_equal = IPv6Address.__eq__(self, other)
- if not address_equal or address_equal is NotImplemented:
+ if address_equal is NotImplemented or not address_equal:
return address_equal
try:
return self.network == other.network
@@ -2109,7 +2109,7 @@
def __lt__(self, other):
address_less = IPv6Address.__lt__(self, other)
if address_less is NotImplemented:
- return NotImplemented
+ return address_less
try:
return (self.network < other.network or
self.network == other.network and address_less)
diff --git a/Lib/test/test_buffer.py b/Lib/test/test_buffer.py
index 6178ffd..2ddca06 100644
--- a/Lib/test/test_buffer.py
+++ b/Lib/test/test_buffer.py
@@ -2528,7 +2528,7 @@
values = [INT(9), IDX(9),
2.2+3j, Decimal("-21.1"), 12.2, Fraction(5, 2),
[1,2,3], {4,5,6}, {7:8}, (), (9,),
- True, False, None, NotImplemented,
+ True, False, None, Ellipsis,
b'a', b'abc', bytearray(b'a'), bytearray(b'abc'),
'a', 'abc', r'a', r'abc',
f, lambda x: x]
diff --git a/Lib/test/test_builtin.py b/Lib/test/test_builtin.py
index 5c553a9..e50c273 100644
--- a/Lib/test/test_builtin.py
+++ b/Lib/test/test_builtin.py
@@ -1666,6 +1666,20 @@
self.assertRaises(TypeError, tp, 1, 2)
self.assertRaises(TypeError, tp, a=1, b=2)
+ def test_warning_notimplemented(self):
+ # Issue #35712: NotImplemented is a sentinel value that should never
+ # be evaluated in a boolean context (virtually all such use cases
+ # are a result of accidental misuse implementing rich comparison
+ # operations in terms of one another).
+ # For the time being, it will continue to evaluate as truthy, but
+ # issue a deprecation warning (with the eventual intent to make it
+ # a TypeError).
+ self.assertWarns(DeprecationWarning, bool, NotImplemented)
+ with self.assertWarns(DeprecationWarning):
+ self.assertTrue(NotImplemented)
+ with self.assertWarns(DeprecationWarning):
+ self.assertFalse(not NotImplemented)
+
class TestBreakpoint(unittest.TestCase):
def setUp(self):
diff --git a/Lib/test/test_descr.py b/Lib/test/test_descr.py
index d2e1218..96cc8de2 100644
--- a/Lib/test/test_descr.py
+++ b/Lib/test/test_descr.py
@@ -2526,9 +2526,9 @@
except TypeError:
pass
- # Two essentially featureless objects, just inheriting stuff from
- # object.
- self.assertEqual(dir(NotImplemented), dir(Ellipsis))
+ # Two essentially featureless objects, (Ellipsis just inherits stuff
+ # from object.
+ self.assertEqual(dir(object()), dir(Ellipsis))
# Nasty test case for proxied objects
class Wrapper(object):
diff --git a/Misc/NEWS.d/next/Core and Builtins/2019-05-08-11-11-45.bpo-35712.KJthus.rst b/Misc/NEWS.d/next/Core and Builtins/2019-05-08-11-11-45.bpo-35712.KJthus.rst
new file mode 100644
index 0000000..3a68632
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2019-05-08-11-11-45.bpo-35712.KJthus.rst
@@ -0,0 +1,2 @@
+Using :data:`NotImplemented` in a boolean context has been deprecated. Patch
+contributed by Josh Rosenberg.
diff --git a/Objects/object.c b/Objects/object.c
index 81de3b8..9c74e07 100644
--- a/Objects/object.c
+++ b/Objects/object.c
@@ -1673,6 +1673,22 @@
Py_FatalError("deallocating NotImplemented");
}
+static int
+notimplemented_bool(PyObject *v)
+{
+ if (PyErr_WarnEx(PyExc_DeprecationWarning,
+ "NotImplemented should not be used in a boolean context",
+ 1) < 0)
+ {
+ return -1;
+ }
+ return 1;
+}
+
+static PyNumberMethods notimplemented_as_number = {
+ .nb_bool = notimplemented_bool,
+};
+
PyTypeObject _PyNotImplemented_Type = {
PyVarObject_HEAD_INIT(&PyType_Type, 0)
"NotImplementedType",
@@ -1683,8 +1699,8 @@
0, /*tp_getattr*/
0, /*tp_setattr*/
0, /*tp_as_async*/
- NotImplemented_repr, /*tp_repr*/
- 0, /*tp_as_number*/
+ NotImplemented_repr, /*tp_repr*/
+ ¬implemented_as_number, /*tp_as_number*/
0, /*tp_as_sequence*/
0, /*tp_as_mapping*/
0, /*tp_hash */