[pull] main from python:main

Doc/library/itertools.rst

@@ -845,7 +845,8 @@ and :term:`generators <generator>` which incur interpreter overhead.
    from contextlib import suppress
    from functools import reduce
    from math import comb, isqrt, prod, sumprod
-   from operator import getitem, is_not, itemgetter, mul, neg
+   from operator import getitem, is_not, itemgetter, mul, neg, truediv
+
 
    # ==== Basic one liners ====
 
@@ -858,9 +859,10 @@ and :term:`generators <generator>` which incur interpreter overhead.
        # prepend(1, [2, 3, 4]) → 1 2 3 4
        return chain([value], iterable)
 
-   def tabulate(function, start=0):
-       "Return function(0), function(1), ..."
-       return map(function, count(start))
+   def running_mean(iterable):
+       "Yield the average of all values seen so far."
+       # running_mean([8.5, 9.5, 7.5, 6.5]) -> 8.5 9.0 8.5 8.0
+       return map(truediv, accumulate(iterable), count(1))
 
    def repeatfunc(function, times=None, *args):
        "Repeat calls to a function with specified arguments."
@@ -913,6 +915,7 @@ and :term:`generators <generator>` which incur interpreter overhead.
        # all_equal('4٤௪౪໔', key=int) → True
        return len(take(2, groupby(iterable, key))) <= 1
 
+
    # ==== Data pipelines ====
 
    def unique_justseen(iterable, key=None):
@@ -1021,6 +1024,7 @@ and :term:`generators <generator>` which incur interpreter overhead.
            while True:
                yield function()
 
+
    # ==== Mathematical operations ====
 
    def multinomial(*counts):
@@ -1040,6 +1044,7 @@ and :term:`generators <generator>` which incur interpreter overhead.
        # sum_of_squares([10, 20, 30]) → 1400
        return sumprod(*tee(iterable))
 
+
    # ==== Matrix operations ====
 
    def reshape(matrix, columns):
@@ -1058,6 +1063,7 @@ and :term:`generators <generator>` which incur interpreter overhead.
        n = len(m2[0])
        return batched(starmap(sumprod, product(m1, transpose(m2))), n)
 
+
    # ==== Polynomial arithmetic ====
 
    def convolve(signal, kernel):
@@ -1114,6 +1120,7 @@ and :term:`generators <generator>` which incur interpreter overhead.
        powers = reversed(range(1, n))
        return list(map(mul, coefficients, powers))
 
+
    # ==== Number theory ====
 
    def sieve(n):
@@ -1230,8 +1237,8 @@ and :term:`generators <generator>` which incur interpreter overhead.
     [(0, 'a'), (1, 'b'), (2, 'c')]
 
 
-    >>> list(islice(tabulate(lambda x: 2*x), 4))
-    [0, 2, 4, 6]
+    >>> list(running_mean([8.5, 9.5, 7.5, 6.5]))
+    [8.5, 9.0, 8.5, 8.0]
 
 
     >>> for _ in loops(5):
@@ -1798,6 +1805,10 @@ and :term:`generators <generator>` which incur interpreter overhead.
 
     # Old recipes and their tests which are guaranteed to continue to work.
 
+    def tabulate(function, start=0):
+        "Return function(0), function(1), ..."
+        return map(function, count(start))
+
     def old_sumprod_recipe(vec1, vec2):
         "Compute a sum of products."
         return sum(starmap(operator.mul, zip(vec1, vec2, strict=True)))
@@ -1877,6 +1888,10 @@ and :term:`generators <generator>` which incur interpreter overhead.
 .. doctest::
     :hide:
 
+    >>> list(islice(tabulate(lambda x: 2*x), 4))
+    [0, 2, 4, 6]
+
+
     >>> dotproduct([1,2,3], [4,5,6])
     32
 

Lib/test/test_free_threading/test_itertools.py

@@ -1,94 +1,59 @@
 import unittest
-from threading import Thread, Barrier
-from itertools import batched, chain, cycle
+from itertools import batched, chain, combinations_with_replacement, cycle, permutations
 from test.support import threading_helper
 
 
 threading_helper.requires_working_threading(module=True)
 
-class ItertoolsThreading(unittest.TestCase):
-
-    @threading_helper.reap_threads
-    def test_batched(self):
-        number_of_threads = 10
-        number_of_iterations = 20
-        barrier = Barrier(number_of_threads)
-        def work(it):
-            barrier.wait()
-            while True:
-                try:
-                    next(it)
-                except StopIteration:
-                    break
 
-        data = tuple(range(1000))
-        for it in range(number_of_iterations):
-            batch_iterator = batched(data, 2)
-            worker_threads = []
-            for ii in range(number_of_threads):
-                worker_threads.append(
-                    Thread(target=work, args=[batch_iterator]))
+def work_iterator(it):
+    while True:
+        try:
+            next(it)
+        except StopIteration:
+            break
 
-            with threading_helper.start_threads(worker_threads):
-                pass
 
-            barrier.reset()
+class ItertoolsThreading(unittest.TestCase):
 
     @threading_helper.reap_threads
-    def test_cycle(self):
-        number_of_threads = 6
+    def test_batched(self):
         number_of_iterations = 10
-        number_of_cycles = 400
+        for _ in range(number_of_iterations):
+            it = batched(tuple(range(1000)), 2)
+            threading_helper.run_concurrently(work_iterator, nthreads=10, args=[it])
 
-        barrier = Barrier(number_of_threads)
+    @threading_helper.reap_threads
+    def test_cycle(self):
         def work(it):
-            barrier.wait()
-            for _ in range(number_of_cycles):
-                try:
-                    next(it)
-                except StopIteration:
-                    pass
+            for _ in range(400):
+                next(it)
 
-        data = (1, 2, 3, 4)
-        for it in range(number_of_iterations):
-            cycle_iterator = cycle(data)
-            worker_threads = []
-            for ii in range(number_of_threads):
-                worker_threads.append(
-                    Thread(target=work, args=[cycle_iterator]))
-
-            with threading_helper.start_threads(worker_threads):
-                pass
-
-            barrier.reset()
+        number_of_iterations = 6
+        for _ in range(number_of_iterations):
+            it = cycle((1, 2, 3, 4))
+            threading_helper.run_concurrently(work, nthreads=6, args=[it])
 
     @threading_helper.reap_threads
     def test_chain(self):
-        number_of_threads = 6
-        number_of_iterations = 20
-
-        barrier = Barrier(number_of_threads)
-        def work(it):
-            barrier.wait()
-            while True:
-                try:
-                    next(it)
-                except StopIteration:
-                    break
-
-        data = [(1, )] * 200
-        for it in range(number_of_iterations):
-            chain_iterator = chain(*data)
-            worker_threads = []
-            for ii in range(number_of_threads):
-                worker_threads.append(
-                    Thread(target=work, args=[chain_iterator]))
-
-            with threading_helper.start_threads(worker_threads):
-                pass
+        number_of_iterations = 10
+        for _ in range(number_of_iterations):
+            it = chain(*[(1,)] * 200)
+            threading_helper.run_concurrently(work_iterator, nthreads=6, args=[it])
 
-            barrier.reset()
+    @threading_helper.reap_threads
+    def test_combinations_with_replacement(self):
+        number_of_iterations = 6
+        for _ in range(number_of_iterations):
+            it = combinations_with_replacement(tuple(range(2)), 2)
+            threading_helper.run_concurrently(work_iterator, nthreads=6, args=[it])
 
+    @threading_helper.reap_threads
+    def test_permutations(self):
+        number_of_iterations = 6
+        for _ in range(number_of_iterations):
+            it = permutations(tuple(range(4)), 2)
+            threading_helper.run_concurrently(work_iterator, nthreads=6, args=[it])
 
 
 if __name__ == "__main__":

Misc/NEWS.d/next/Library/2026-02-03-08-50-58.gh-issue-123471.yF1Gym.rst

@@ -0,0 +1 @@
+Make concurrent iteration over :class:`itertools.combinations_with_replacement` and :class:`itertools.permutations` safe under free-threading.

Modules/itertoolsmodule.c

@@ -2587,7 +2587,7 @@ cwr_traverse(PyObject *op, visitproc visit, void *arg)
 }
 
 static PyObject *
-cwr_next(PyObject *op)
+cwr_next_lock_held(PyObject *op)
 {
     cwrobject *co = cwrobject_CAST(op);
     PyObject *elem;
@@ -2666,6 +2666,16 @@ cwr_next(PyObject *op)
     return NULL;
 }
 
+static PyObject *
+cwr_next(PyObject *op)
+{
+    PyObject *result;
+    Py_BEGIN_CRITICAL_SECTION(op);
+    result = cwr_next_lock_held(op);
+    Py_END_CRITICAL_SECTION()
+    return result;
+}
+
 static PyMethodDef cwr_methods[] = {
     {"__sizeof__", cwr_sizeof, METH_NOARGS, sizeof_doc},
     {NULL,              NULL}   /* sentinel */
@@ -2846,7 +2856,7 @@ permutations_traverse(PyObject *op, visitproc visit, void *arg)
 }
 
 static PyObject *
-permutations_next(PyObject *op)
+permutations_next_lock_held(PyObject *op)
 {
     permutationsobject *po = permutationsobject_CAST(op);
     PyObject *elem;
@@ -2936,6 +2946,16 @@ permutations_next(PyObject *op)
     return NULL;
 }
 
+static PyObject *
+permutations_next(PyObject *op)
+{
+    PyObject *result;
+    Py_BEGIN_CRITICAL_SECTION(op);
+    result = permutations_next_lock_held(op);
+    Py_END_CRITICAL_SECTION()
+    return result;
+}
+
 static PyMethodDef permuations_methods[] = {
     {"__sizeof__", permutations_sizeof, METH_NOARGS, sizeof_doc},
     {NULL,              NULL}   /* sentinel */