python · warsaw · Sep 8, 2017 · Sep 10, 2017 · Sep 10, 2017 · Sep 10, 2017
diff --git a/Doc/library/functions.rst b/Doc/library/functions.rst
@@ -10,20 +10,20 @@ are always available.  They are listed here in alphabetical order.
 ===================  =================  ==================  ================  ====================
 ..                   ..                 Built-in Functions  ..                ..
 ===================  =================  ==================  ================  ====================
-:func:`abs`          |func-dict|_       :func:`help`        :func:`min`       :func:`setattr`
-:func:`all`          :func:`dir`        :func:`hex`         :func:`next`      :func:`slice`
-:func:`any`          :func:`divmod`     :func:`id`          :func:`object`    :func:`sorted`
-:func:`ascii`        :func:`enumerate`  :func:`input`       :func:`oct`       :func:`staticmethod`
-:func:`bin`          :func:`eval`       :func:`int`         :func:`open`      |func-str|_
-:func:`bool`         :func:`exec`       :func:`isinstance`  :func:`ord`       :func:`sum`
-|func-bytearray|_    :func:`filter`     :func:`issubclass`  :func:`pow`       :func:`super`
-|func-bytes|_        :func:`float`      :func:`iter`        :func:`print`     |func-tuple|_
-:func:`callable`     :func:`format`     :func:`len`         :func:`property`  :func:`type`
-:func:`chr`          |func-frozenset|_  |func-list|_        |func-range|_     :func:`vars`
-:func:`classmethod`  :func:`getattr`    :func:`locals`      :func:`repr`      :func:`zip`
-:func:`compile`      :func:`globals`    :func:`map`         :func:`reversed`  :func:`__import__`
-:func:`complex`      :func:`hasattr`    :func:`max`         :func:`round`
-:func:`delattr`      :func:`hash`       |func-memoryview|_  |func-set|_
+:func:`abs`          |func-dict|_       :func:`help`        :func:`min`       |func-set|_
+:func:`all`          :func:`dir`        :func:`hex`         :func:`next`      :func:`setattr`
+:func:`any`          :func:`divmod`     :func:`id`          :func:`noop`      :func:`slice`
+:func:`ascii`        :func:`enumerate`  :func:`input`       :func:`object`    :func:`sorted`
+:func:`bin`          :func:`eval`       :func:`int`         :func:`oct`       :func:`staticmethod`
+:func:`bool`         :func:`exec`       :func:`isinstance`  :func:`open`      |func-str|_
+|func-bytearray|_    :func:`filter`     :func:`issubclass`  :func:`ord`       :func:`sum`
+|func-bytes|_        :func:`float`      :func:`iter`        :func:`pow`       :func:`super`
+:func:`callable`     :func:`format`     :func:`len`         :func:`print`     |func-tuple|_
+:func:`chr`          |func-frozenset|_  |func-list|_        :func:`property`  :func:`type`
+:func:`classmethod`  :func:`getattr`    :func:`locals`      |func-range|_     :func:`vars`
+:func:`compile`      :func:`globals`    :func:`map`         :func:`repr`      :func:`zip`
+:func:`complex`      :func:`hasattr`    :func:`max`         :func:`reversed`  :func:`__import__`
+:func:`delattr`      :func:`hash`       |func-memoryview|_  :func:`round`
 ===================  =================  ==================  ================  ====================
 
 .. using :func:`dict` would create a link to another page, so local targets are
@@ -889,6 +889,12 @@ are always available.  They are listed here in alphabetical order.
    if the iterator is exhausted, otherwise :exc:`StopIteration` is raised.
 
 
+.. function:: noop(*args, **kws)
+
+   Do nothing but return ``None``.
+
+   .. versionadded:: 3.7
+
 .. class:: object()
 
    Return a new featureless object.  :class:`object` is a base for all classes.

diff --git a/Lib/test/test_builtin.py b/Lib/test/test_builtin.py
@@ -984,6 +984,14 @@ def gen():
         self.assertRaises(StopIteration, next, it)
         self.assertEqual(next(it, 42), 42)
 
+    def test_noop(self):
+        self.assertIsNone(noop())
+        self.assertIsNone(noop(1))
+        self.assertIsNone(noop(1, 2))
+        self.assertIsNone(noop(a=1))
+        self.assertIsNone(noop(a=1, b=3))
+        self.assertIsNone(noop(2, 4, a=1, b=3))
+
     def test_oct(self):
         self.assertEqual(oct(100), '0o144')
         self.assertEqual(oct(-100), '-0o144')

diff --git a/Lib/test/test_inspect.py b/Lib/test/test_inspect.py
@@ -2018,7 +2018,7 @@ def test_staticmethod(*args):  # NOQA
                          ((('args', ..., ..., 'var_positional'),), ...))
         self.assertEqual(self.signature(A.f3),
                          ((('args', ..., ..., 'var_positional'),), ...))
-        self.assertEqual(self.signature(A.f4), 
+        self.assertEqual(self.signature(A.f4),
                          ((('args', ..., ..., 'var_positional'),
                             ('kwargs', ..., ..., 'var_keyword')), ...))
     @cpython_only
@@ -3523,7 +3523,7 @@ def test_builtins_have_signatures(self):
         needs_semantic_update = {"round"}
         no_signature |= needs_semantic_update
         # These need *args support in Argument Clinic
-        needs_varargs = {"min", "max", "print", "__build_class__"}
+        needs_varargs = {"min", "max", "noop", "print", "__build_class__"}
         no_signature |= needs_varargs
         # These simply weren't covered in the initial AC conversion
         # for builtin callables

diff --git a/Misc/NEWS.d/next/Core and Builtins/2017-09-10-09-59-48.bpo-31409.3zS7xH.rst b/Misc/NEWS.d/next/Core and Builtins/2017-09-10-09-59-48.bpo-31409.3zS7xH.rst
@@ -0,0 +1 @@
+PEP 559 - Built-in noop() function.
diff --git a/Python/bltinmodule.c b/Python/bltinmodule.c
@@ -1337,6 +1337,19 @@ Return the next item from the iterator. If default is given and the iterator\n\
 is exhausted, it is returned instead of raising StopIteration.");
 
 
+static PyObject *
+builtin_noop(PyObject *self, PyObject *args, PyObject *keywords)
+{
+    Py_RETURN_NONE;
+}
+
+
+PyDoc_STRVAR(noop_doc,
+"noop(*args, **kws)\n\
+\n\
+Do nothing except return None.");
+
+
 /*[clinic input]
 setattr as builtin_setattr
 
@@ -2644,6 +2657,7 @@ static PyMethodDef builtin_methods[] = {
     {"max",             (PyCFunction)builtin_max,        METH_VARARGS | METH_KEYWORDS, max_doc},
     {"min",             (PyCFunction)builtin_min,        METH_VARARGS | METH_KEYWORDS, min_doc},
     {"next",            (PyCFunction)builtin_next,       METH_FASTCALL, next_doc},
+    {"noop",            (PyCFunction)builtin_noop,       METH_VARARGS | METH_KEYWORDS, noop_doc},
     BUILTIN_OCT_METHODDEF
     BUILTIN_ORD_METHODDEF
     BUILTIN_POW_METHODDEF