https://github.com/python/cpython/commit/3a62c8f13ab9ab0373fe2bf675b02708cf4f6a6e
commit: 3a62c8f13ab9ab0373fe2bf675b02708cf4f6a6e
branch: main
author: sobolevn <[email protected]>
committer: Eclips4 <[email protected]>
date: 2026-05-08T18:34:48+03:00
summary:
gh-149537: Remove kw parameters from python version of `reduce` (#149538)
files:
A Misc/NEWS.d/next/Library/2026-05-08-08-24-01.gh-issue-149537.hVFVnt.rst
M Doc/whatsnew/3.16.rst
M Lib/functools.py
M Lib/test/test_functools.py
diff --git a/Doc/whatsnew/3.16.rst b/Doc/whatsnew/3.16.rst
index 98a8644884a8d7..4ddc836d9b29e4 100644
--- a/Doc/whatsnew/3.16.rst
+++ b/Doc/whatsnew/3.16.rst
@@ -114,6 +114,12 @@ annotationlib
Use :meth:`annotationlib.ForwardRef.evaluate`
or :func:`typing.evaluate_forward_ref` instead.
+functools
+---------
+
+* Calling the Python implementation of :func:`functools.reduce` with *function*
+ or *sequence* as keyword arguments has been deprecated since Python 3.14.
+
sysconfig
---------
diff --git a/Lib/functools.py b/Lib/functools.py
index cd374631f16792..73274b94ef37da 100644
--- a/Lib/functools.py
+++ b/Lib/functools.py
@@ -234,7 +234,7 @@ def __ge__(self, other):
_initial_missing = object()
-def reduce(function, sequence, initial=_initial_missing):
+def reduce(function, sequence, /, initial=_initial_missing):
"""
reduce(function, iterable, /[, initial]) -> value
@@ -264,6 +264,11 @@ def reduce(function, sequence, initial=_initial_missing):
return value
+try:
+ from _functools import reduce
+except ImportError:
+ pass
+
################################################################################
### partial() argument application
@@ -1178,31 +1183,3 @@ def __get__(self, instance, owner=None):
return val
__class_getitem__ = classmethod(GenericAlias)
-
-def _warn_python_reduce_kwargs(py_reduce):
- @wraps(py_reduce)
- def wrapper(*args, **kwargs):
- if 'function' in kwargs or 'sequence' in kwargs:
- import os
- import warnings
- warnings.warn(
- 'Calling functools.reduce with keyword arguments '
- '"function" or "sequence" '
- 'is deprecated in Python 3.14 and will be '
- 'forbidden in Python 3.16.',
- DeprecationWarning,
- skip_file_prefixes=(os.path.dirname(__file__),))
- return py_reduce(*args, **kwargs)
- return wrapper
-
-reduce = _warn_python_reduce_kwargs(reduce)
-del _warn_python_reduce_kwargs
-
-# The import of the C accelerated version of reduce() has been moved
-# here due to gh-121676. In Python 3.16, _warn_python_reduce_kwargs()
-# should be removed and the import block should be moved back right
-# after the definition of reduce().
-try:
- from _functools import reduce
-except ImportError:
- pass
diff --git a/Lib/test/test_functools.py b/Lib/test/test_functools.py
index a8ee7d119e4bc6..c30386afe41849 100644
--- a/Lib/test/test_functools.py
+++ b/Lib/test/test_functools.py
@@ -1134,6 +1134,14 @@ def add(x, y):
self.assertRaises(TypeError, self.reduce, add, [0, 1], initial="")
self.assertEqual(self.reduce(42, "", initial="1"), "1") # func is
never called with one item
+ def test_reduce_with_kwargs(self):
+ with self.assertRaises(TypeError):
+ self.reduce(function=lambda x, y: (x or 1) + y, sequence=[1, 2, 3,
4, 5])
+ with self.assertRaises(TypeError):
+ self.reduce(function=lambda x, y: x + y, sequence=[1, 2, 3, 4, 5],
initial=1)
+ with self.assertRaises(TypeError):
+ self.reduce(lambda x, y: x + y, sequence=[1, 2, 3, 4, 5],
initial=1)
+
@unittest.skipUnless(c_functools, 'requires the C _functools module')
class TestReduceC(TestReduce, unittest.TestCase):
@@ -1144,12 +1152,6 @@ class TestReduceC(TestReduce, unittest.TestCase):
class TestReducePy(TestReduce, unittest.TestCase):
reduce = staticmethod(py_functools.reduce)
- def test_reduce_with_kwargs(self):
- with self.assertWarns(DeprecationWarning):
- self.reduce(function=lambda x, y: x + y, sequence=[1, 2, 3, 4, 5],
initial=1)
- with self.assertWarns(DeprecationWarning):
- self.reduce(lambda x, y: x + y, sequence=[1, 2, 3, 4, 5],
initial=1)
-
class TestCmpToKey:
diff --git
a/Misc/NEWS.d/next/Library/2026-05-08-08-24-01.gh-issue-149537.hVFVnt.rst
b/Misc/NEWS.d/next/Library/2026-05-08-08-24-01.gh-issue-149537.hVFVnt.rst
new file mode 100644
index 00000000000000..2fb0359a2ea893
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-05-08-08-24-01.gh-issue-149537.hVFVnt.rst
@@ -0,0 +1,2 @@
+Remove kw parameters from python version of :func:`functools.reduce`
+function.
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