[pull] main from python:main

Doc/c-api/float.rst

@@ -201,8 +201,8 @@ NaNs (if such things exist on the platform) isn't handled correctly, and
 attempting to unpack a bytes string containing an IEEE INF or NaN will raise an
 exception.
 
-Note that NaNs type may not be preserved on IEEE platforms (signaling NaN become
-quiet NaN), for example on x86 systems in 32-bit mode.
+Note that NaN type may not be preserved on IEEE platforms (signaling NaNs become
+quiet NaNs), for example on x86 systems in 32-bit mode.
 
 On non-IEEE platforms with more precision, or larger dynamic range, than IEEE
 754 supports, not all values can be packed; on non-IEEE platforms with less
@@ -216,7 +216,7 @@ Pack functions
 
 The pack routines write 2, 4 or 8 bytes, starting at *p*. *le* is an
 :c:expr:`int` argument, non-zero if you want the bytes string in little-endian
-format (exponent last, at ``p+1``, ``p+3``, or ``p+6`` ``p+7``), zero if you
+format (exponent last, at ``p+1``, ``p+3``, or ``p+6`` and ``p+7``), zero if you
 want big-endian format (exponent first, at *p*). The :c:macro:`PY_BIG_ENDIAN`
 constant can be used to use the native endian: it is equal to ``1`` on big
 endian processor, or ``0`` on little endian processor.

Doc/whatsnew/3.15.rst

@@ -1286,11 +1286,11 @@ Upgraded JIT compiler
 
 Results from the `pyperformance <https://github.com/python/pyperformance>`__
 benchmark suite report
-`4-5% <https://raw.githubusercontent.com/facebookexperimental/free-threading-benchmarking/refs/heads/main/results/bm-20260110-3.15.0a3%2B-aa8578d-JIT/bm-20260110-vultr-x86_64-python-aa8578dc54df2af9daa3-3.15.0a3%2B-aa8578d-vs-base.svg>`__
+`5-6% <https://doesjitgobrrr.com/run/2026-03-11>`__
 geometric mean performance improvement for the JIT over the standard CPython
 interpreter built with all optimizations enabled on x86-64 Linux. On AArch64
 macOS, the JIT has a
-`7-8% <https://raw.githubusercontent.com/facebookexperimental/free-threading-benchmarking/refs/heads/main/results/bm-20260110-3.15.0a3%2B-aa8578d-JIT/bm-20260110-macm4pro-arm64-python-aa8578dc54df2af9daa3-3.15.0a3%2B-aa8578d-vs-base.svg>`__
+`8-9% <https://doesjitgobrrr.com/run/2026-03-11>`__
 speedup over the :ref:`tail calling interpreter <whatsnew314-tail-call-interpreter>`
 with all optimizations enabled. The speedups for JIT
 builds versus no JIT builds range from roughly 15% slowdown to over

Lib/multiprocessing/context.py

@@ -145,7 +145,13 @@ def freeze_support(self):
         '''Check whether this is a fake forked process in a frozen executable.
         If so then run code specified by commandline and exit.
         '''
-        if self.get_start_method() == 'spawn' and getattr(sys, 'frozen', False):
+        # gh-140814: allow_none=True avoids locking in the default start
+        # method, which would cause a later set_start_method() to fail.
+        # None is safe to pass through: spawn.freeze_support()
+        # independently detects whether this process is a spawned
+        # child, so the start method check here is only an optimization.
+        if (getattr(sys, 'frozen', False)
+                and self.get_start_method(allow_none=True) in ('spawn', None)):
             from .spawn import freeze_support
             freeze_support()
 

Lib/test/_test_multiprocessing.py

@@ -6005,6 +6005,20 @@ def test_spawn_dont_set_context(self):
             process.join()
             self.assertIsNone(multiprocessing.get_start_method(allow_none=True))
 
+    @only_run_in_spawn_testsuite("freeze_support is not start method specific")
+    def test_freeze_support_dont_set_context(self):
+        # gh-140814: freeze_support() should not set the start method
+        # as a side effect, so a later set_start_method() still works.
+        multiprocessing.set_start_method(None, force=True)
+        try:
+            multiprocessing.freeze_support()
+            self.assertIsNone(
+                multiprocessing.get_start_method(allow_none=True))
+            # Should not raise "context has already been set"
+            multiprocessing.set_start_method('spawn')
+        finally:
+            multiprocessing.set_start_method(None, force=True)
+
     def test_context_check_module_types(self):
         try:
             ctx = multiprocessing.get_context('forkserver')

Lib/test/test_capi/test_misc.py

@@ -916,6 +916,18 @@ def genf(): yield
         gen = genf()
         self.assertEqual(_testcapi.gen_get_code(gen), gen.gi_code)
 
+    def test_tp_bases_slot(self):
+        cls = _testcapi.HeapCTypeWithBasesSlot
+        self.assertEqual(cls.__bases__, (int,))
+        self.assertEqual(cls.__base__, int)
+
+    def test_tp_bases_slot_none(self):
+        self.assertRaisesRegex(
+            SystemError,
+            "Py_tp_bases is not a tuple",
+            _testcapi.create_heapctype_with_none_bases_slot
+        )
+
 
 @requires_limited_api
 class TestHeapTypeRelative(unittest.TestCase):

Lib/test/test_free_threading/test_itertools.py

@@ -1,5 +1,5 @@
 import unittest
-from itertools import batched, chain, combinations_with_replacement, cycle, permutations
+from itertools import accumulate, batched, chain, combinations_with_replacement, cycle, permutations
 from test.support import threading_helper
 
 
@@ -16,6 +16,13 @@ def work_iterator(it):
 
 class ItertoolsThreading(unittest.TestCase):
 
+    @threading_helper.reap_threads
+    def test_accumulate(self):
+        number_of_iterations = 10
+        for _ in range(number_of_iterations):
+            it = accumulate(tuple(range(40)))
+            threading_helper.run_concurrently(work_iterator, nthreads=10, args=[it])
+
     @threading_helper.reap_threads
     def test_batched(self):
         number_of_iterations = 10

Misc/NEWS.d/next/Documentation/2026-03-09-00-00-00.gh-issue-145649.8BcbAB.rst

@@ -0,0 +1,2 @@
+Fix text wrapping and formatting of ``-X`` option descriptions in the
+:manpage:`python(1)` man page by using proper roff markup.

Misc/NEWS.d/next/Library/2026-02-04-20-30-59.gh-issue-123471.1dnPvs.rst

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

Misc/NEWS.d/next/Library/2026-02-08-22-04-06.gh-issue-140814.frzSpn.rst

@@ -0,0 +1,3 @@
+:func:`multiprocessing.freeze_support` no longer sets the default start method
+as a side effect, which previously caused a subsequent
+:func:`multiprocessing.set_start_method` call to raise :exc:`RuntimeError`.

Misc/python.man

@@ -320,82 +320,105 @@ a regular expression on the warning message.
 .TP
 .BI "\-X " option
 Set implementation-specific option. The following options are available:
-
-    \fB\-X cpu_count=\fIN\fR: override the return value of \fIos.cpu_count()\fR;
-       \fB\-X cpu_count=default\fR cancels overriding; also \fBPYTHON_CPU_COUNT\fI
-
-    \fB\-X dev\fR: enable CPython's "development mode", introducing additional
-        runtime checks which are too expensive to be enabled by default. It
-        will not be more verbose than the default if the code is correct: new
-        warnings are only emitted when an issue is detected. Effect of the
-        developer mode:
-           * Add default warning filter, as \fB\-W default\fR
-           * Install debug hooks on memory allocators: see the
-             PyMem_SetupDebugHooks() C function
-           * Enable the faulthandler module to dump the Python traceback on a
-             crash
-           * Enable asyncio debug mode
-           * Set the dev_mode attribute of sys.flags to True
-           * io.IOBase destructor logs close() exceptions
-
-    \fB\-X importtime\fR: show how long each import takes. It shows module name,
-        cumulative time (including nested imports) and self time (excluding
-        nested imports). Note that its output may be broken in multi-threaded
-        application. Typical usage is
-        \fBpython3 \-X importtime \-c 'import asyncio'\fR
-
-        \fB\-X importtime=2\fR enables additional output that indicates when an
-        imported module has already been loaded.  In such cases, the string
-        \fBcached\fR will be printed in both time columns.
-
-    \fB\-X faulthandler\fR: enable faulthandler
-
-    \fB\-X frozen_modules=\fR[\fBon\fR|\fBoff\fR]: whether or not frozen modules
-       should be used.
-       The default is "on" (or "off" if you are running a local build).
-
-    \fB\-X gil=\fR[\fB0\fR|\fB1\fR]: enable (1) or disable (0) the GIL; also
-       \fBPYTHON_GIL\fR
-       Only available in builds configured with \fB\-\-disable\-gil\fR.
-
-    \fB\-X int_max_str_digits=\fInumber\fR: limit the size of int<->str conversions.
-       This helps avoid denial of service attacks when parsing untrusted data.
-       The default is sys.int_info.default_max_str_digits.  0 disables.
-
-    \fB\-X no_debug_ranges\fR: disable the inclusion of the tables mapping extra
-       location information (end line, start column offset and end column
-       offset) to every instruction in code objects. This is useful when
-       smaller code objects and pyc files are desired as well as suppressing
-       the extra visual location indicators when the interpreter displays
-       tracebacks.
-
-    \fB\-X perf\fR: support the Linux "perf" profiler; also \fBPYTHONPERFSUPPORT=1\fR
-
-    \fB\-X perf_jit\fR: support the Linux "perf" profiler with DWARF support;
-       also \fBPYTHON_PERF_JIT_SUPPORT=1\fR
-
-    \fB\-X presite=\fIMOD\fR: import this module before site; also \fBPYTHON_PRESITE\fR
-       This only works on debug builds.
-
-    \fB\-X pycache_prefix=\fIPATH\fR: enable writing .pyc files to a parallel
-       tree rooted at the given directory instead of to the code tree.
-
-    \fB\-X showrefcount\fR: output the total reference count and number of used
-        memory blocks when the program finishes or after each statement in the
-        interactive interpreter. This only works on debug builds
-
-    \fB\-X tracemalloc\fR: start tracing Python memory allocations using the
-        tracemalloc module. By default, only the most recent frame is stored in a
-        traceback of a trace. Use \-X tracemalloc=NFRAME to start tracing with a
-        traceback limit of NFRAME frames
-
-    \fB\-X utf8\fR: enable UTF-8 mode for operating system interfaces,
-        overriding the default locale-aware mode. \fB\-X utf8=0\fR explicitly
-        disables UTF-8 mode (even when it would otherwise activate
-        automatically). See \fBPYTHONUTF8\fR for more details
-
-    \fB\-X warn_default_encoding\fR: enable opt-in EncodingWarning for 'encoding=None'
-
+.RS
+.TP
+\fB\-X cpu_count=\fIN\fR
+Override the return value of \fIos.cpu_count()\fR.
+\fB\-X cpu_count=default\fR cancels overriding.
+See also \fBPYTHON_CPU_COUNT\fR.
+.TP
+\fB\-X dev\fR
+Enable CPython's "development mode", introducing additional
+runtime checks which are too expensive to be enabled by default. It
+will not be more verbose than the default if the code is correct: new
+warnings are only emitted when an issue is detected. Effect of the
+developer mode:
+.RS
+.IP \(bu 2
+Add default warning filter, as \fB\-W default\fR.
+.IP \(bu 2
+Install debug hooks on memory allocators: see the
+PyMem_SetupDebugHooks() C function.
+.IP \(bu 2
+Enable the faulthandler module to dump the Python traceback on a crash.
+.IP \(bu 2
+Enable asyncio debug mode.
+.IP \(bu 2
+Set the dev_mode attribute of sys.flags to True.
+.IP \(bu 2
+io.IOBase destructor logs close() exceptions.
+.RE
+.TP
+\fB\-X importtime\fR
+Show how long each import takes. It shows module name,
+cumulative time (including nested imports) and self time (excluding
+nested imports). Note that its output may be broken in multi-threaded
+application. Typical usage is
+\fBpython3 \-X importtime \-c 'import asyncio'\fR.
+.IP
+\fB\-X importtime=2\fR enables additional output that indicates when an
+imported module has already been loaded. In such cases, the string
+\fBcached\fR will be printed in both time columns.
+.TP
+\fB\-X faulthandler\fR
+Enable faulthandler.
+.TP
+\fB\-X frozen_modules=\fR[\fBon\fR|\fBoff\fR]
+Whether or not frozen modules should be used.
+The default is "on" (or "off" if you are running a local build).
+.TP
+\fB\-X gil=\fR[\fB0\fR|\fB1\fR]
+Enable (1) or disable (0) the GIL. See also \fBPYTHON_GIL\fR.
+Only available in builds configured with \fB\-\-disable\-gil\fR.
+.TP
+\fB\-X int_max_str_digits=\fInumber\fR
+Limit the size of int<->str conversions.
+This helps avoid denial of service attacks when parsing untrusted data.
+The default is sys.int_info.default_max_str_digits. 0 disables.
+.TP
+\fB\-X no_debug_ranges\fR
+Disable the inclusion of the tables mapping extra
+location information (end line, start column offset and end column
+offset) to every instruction in code objects. This is useful when
+smaller code objects and pyc files are desired as well as suppressing
+the extra visual location indicators when the interpreter displays
+tracebacks.
+.TP
+\fB\-X perf\fR
+Support the Linux "perf" profiler. See also \fBPYTHONPERFSUPPORT=1\fR.
+.TP
+\fB\-X perf_jit\fR
+Support the Linux "perf" profiler with DWARF support.
+See also \fBPYTHON_PERF_JIT_SUPPORT=1\fR.
+.TP
+\fB\-X presite=\fIMOD\fR
+Import this module before site. See also \fBPYTHON_PRESITE\fR.
+This only works on debug builds.
+.TP
+\fB\-X pycache_prefix=\fIPATH\fR
+Enable writing .pyc files to a parallel
+tree rooted at the given directory instead of to the code tree.
+.TP
+\fB\-X showrefcount\fR
+Output the total reference count and number of used
+memory blocks when the program finishes or after each statement in the
+interactive interpreter. This only works on debug builds.
+.TP
+\fB\-X tracemalloc\fR
+Start tracing Python memory allocations using the
+tracemalloc module. By default, only the most recent frame is stored in a
+traceback of a trace. Use \fB\-X tracemalloc=\fINFRAME\fR to start tracing with a
+traceback limit of NFRAME frames.
+.TP
+\fB\-X utf8\fR
+Enable UTF-8 mode for operating system interfaces,
+overriding the default locale-aware mode. \fB\-X utf8=0\fR explicitly
+disables UTF-8 mode (even when it would otherwise activate
+automatically). See \fBPYTHONUTF8\fR for more details.
+.TP
+\fB\-X warn_default_encoding\fR
+Enable opt-in EncodingWarning for 'encoding=None'.
+.RE
 .TP
 .B \-x
 Skip the first line of the source.  This is intended for a DOS

Modules/_testcapi/heaptype.c

@@ -543,6 +543,25 @@ pytype_getmodulebytoken(PyObject *self, PyObject *args)
     return PyType_GetModuleByToken((PyTypeObject *)type, token);
 }
 
+static PyType_Slot HeapCTypeWithBasesSlotNone_slots[] = {
+    {Py_tp_bases, NULL},  /* filled out with Py_None in runtime */
+    {0, 0},
+};
+
+static PyType_Spec HeapCTypeWithBasesSlotNone_spec = {
+    .name = "_testcapi.HeapCTypeWithBasesSlotNone",
+    .basicsize = sizeof(PyObject),
+    .flags = Py_TPFLAGS_DEFAULT,
+    .slots = HeapCTypeWithBasesSlotNone_slots
+};
+
+static PyObject *
+create_heapctype_with_none_bases_slot(PyObject *self, PyObject *Py_UNUSED(ignored))
+{
+    HeapCTypeWithBasesSlotNone_slots[0].pfunc = Py_None;
+    return PyType_FromSpec(&HeapCTypeWithBasesSlotNone_spec);
+}
+
 
 static PyMethodDef TestMethods[] = {
     {"pytype_fromspec_meta",    pytype_fromspec_meta,            METH_O},
@@ -562,6 +581,8 @@ static PyMethodDef TestMethods[] = {
     {"pytype_getbasebytoken", pytype_getbasebytoken, METH_VARARGS},
     {"pytype_getmodulebydef", pytype_getmodulebydef, METH_O},
     {"pytype_getmodulebytoken", pytype_getmodulebytoken, METH_VARARGS},
+    {"create_heapctype_with_none_bases_slot",
+        create_heapctype_with_none_bases_slot, METH_NOARGS},
     {NULL},
 };
 
@@ -892,6 +913,18 @@ static PyType_Spec HeapCTypeMetaclassNullNew_spec = {
     .slots = empty_type_slots
 };
 
+static PyType_Slot HeapCTypeWithBasesSlot_slots[] = {
+    {Py_tp_bases, NULL},  /* filled out in module init function */
+    {0, 0},
+};
+
+static PyType_Spec HeapCTypeWithBasesSlot_spec = {
+    .name = "_testcapi.HeapCTypeWithBasesSlot",
+    .basicsize = sizeof(PyLongObject),
+    .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
+    .slots = HeapCTypeWithBasesSlot_slots
+};
+
 
 typedef struct {
     PyObject_HEAD
@@ -1432,6 +1465,18 @@ _PyTestCapi_Init_Heaptype(PyObject *m) {
         &PyType_Type, m, &HeapCTypeMetaclassNullNew_spec, (PyObject *) &PyType_Type);
     ADD("HeapCTypeMetaclassNullNew", HeapCTypeMetaclassNullNew);
 
+    PyObject *bases = PyTuple_Pack(1, &PyLong_Type);
+    if (bases == NULL) {
+        return -1;
+    }
+    HeapCTypeWithBasesSlot_slots[0].pfunc = bases;
+    PyObject *HeapCTypeWithBasesSlot = PyType_FromSpec(&HeapCTypeWithBasesSlot_spec);
+    Py_DECREF(bases);
+    if (HeapCTypeWithBasesSlot == NULL) {
+        return -1;
+    }
+    ADD("HeapCTypeWithBasesSlot", HeapCTypeWithBasesSlot);
+
     ADD("Py_TP_USE_SPEC", PyLong_FromVoidPtr(Py_TP_USE_SPEC));
 
     PyObject *HeapCCollection = PyType_FromMetaclass(

Modules/itertoolsmodule.c

@@ -3073,7 +3073,7 @@ accumulate_traverse(PyObject *op, visitproc visit, void *arg)
 }
 
 static PyObject *
-accumulate_next(PyObject *op)
+accumulate_next_lock_held(PyObject *op)
 {
     accumulateobject *lz = accumulateobject_CAST(op);
     PyObject *val, *newtotal;
@@ -3105,6 +3105,16 @@ accumulate_next(PyObject *op)
     return newtotal;
 }
 
+static PyObject *
+accumulate_next(PyObject *op)
+{
+    PyObject *result;
+    Py_BEGIN_CRITICAL_SECTION(op);
+    result = accumulate_next_lock_held(op);
+    Py_END_CRITICAL_SECTION()
+    return result;
+}
+
 static PyType_Slot accumulate_slots[] = {
     {Py_tp_dealloc, accumulate_dealloc},
     {Py_tp_getattro, PyObject_GenericGetAttr},