Sync pre-release CPython main branch from GitHub (2026-06-13)

Summary:
Imported python/cpython `3.16.0a0` from upstream rev [`6ce088e`](https://www.github.com/python/cpython/commit/6ce088e20a13ac25320d94c5775bb1a4edc75ba4) (committed 2026-06-13 23:10:56+00:00).

# Commit Info

- Base: (`3.16.0a0`) - [`f4f1020`](https://www.github.com/python/cpython/commit/f4f102027a9b0edc72a048f17b696aa92d2e6893) (commit date: 2026-06-12 16:02:33+00:00)
- Imported: (`3.16.0a0`) - [`6ce088e`](https://www.github.com/python/cpython/commit/6ce088e20a13ac25320d94c5775bb1a4edc75ba4) (commit date: 2026-06-13 23:10:56+00:00)

# Noteworthy file changes

- Low-signal files (3 added) (NEWS.d, docs, .github)

Complete list of added/removed files: https://www.internalfb.com/intern/everpaste/?color=0&handle=GLz10CGUHEycsYcEAEL3X518xt8Sbr0LAAAz

Differential Revision: D108538185

fbshipit-source-id: faafbff06a5815fdedf5187b94c8bd32f9405adb

Author: generatedunixname1734921407115435

Doc/library/enum.rst

@@ -629,7 +629,7 @@ Data types
          >>> white in purple
          False
 
-   .. method:: __iter__(self):
+   .. method:: __iter__(self)
 
       Returns all contained non-alias members::
 
@@ -640,7 +640,7 @@ Data types
 
       .. versionadded:: 3.11
 
-   .. method:: __len__(self):
+   .. method:: __len__(self)
 
       Returns number of members in flag::
 
@@ -651,7 +651,7 @@ Data types
 
       .. versionadded:: 3.11
 
-   .. method:: __bool__(self):
+   .. method:: __bool__(self)
 
       Returns *True* if any members in flag, *False* otherwise::
 
@@ -688,7 +688,7 @@ Data types
          >>> purple ^ Color.GREEN
          <Color.RED|GREEN|BLUE: 7>
 
-   .. method:: __invert__(self):
+   .. method:: __invert__(self)
 
       Returns all the flags in *type(self)* that are not in *self*::
 

Doc/library/unittest.mock.rst

@@ -2539,7 +2539,7 @@ Alternatively you can just use ``vars(my_mock)`` (instance members) and
 mock_open
 ~~~~~~~~~
 
-.. function:: mock_open(mock=None, read_data=None)
+.. function:: mock_open(mock=None, read_data='')
 
    A helper function to create a mock to replace the use of :func:`open`. It works
    for :func:`open` called directly or used as a context manager.

Lib/base64.py

@@ -1,4 +1,4 @@
-"""Base16, Base32, Base64 (RFC 3548), Base85 and Ascii85 data encodings"""
+"""Base16, Base32, Base64 (RFC 4648), Base85 and Ascii85 data encodings"""
 
 # Modified 04-Oct-1995 by Jack Jansen to use binascii module
 # Modified 30-Dec-2003 by Barry Warsaw to add full RFC 3548 support
@@ -219,7 +219,7 @@ def urlsafe_b64decode(s, *, padded=False):
 characters present in the input.
 '''
 _B32_DECODE_MAP01_DOCSTRING = '''
-RFC 3548 allows for optional mapping of the digit 0 (zero) to the
+RFC 4648 allows for optional mapping of the digit 0 (zero) to the
 letter O (oh), and for optional mapping of the digit 1 (one) to
 either the letter I (eye) or letter L (el).  The optional argument
 map01 when not None, specifies which letter the digit 1 should be
@@ -266,7 +266,7 @@ def b32hexdecode(s, casefold=False, *, padded=True, ignorechars=b'',
                                                     extra_args='')
 
 
-# RFC 3548, Base 16 Alphabet specifies uppercase, but hexlify() returns
+# RFC 4648, Base 16 Alphabet specifies uppercase, but hexlify() returns
 # lowercase.  The RFC also recommends against accepting input case
 # insensitively.
 def b16encode(s, *, wrapcol=0):

Lib/concurrent/futures/process.py

@@ -469,11 +469,9 @@ def _terminate_broken(self, cause):
             executor._shutdown_thread = True
             executor = None
 
-        # All pending tasks are to be marked failed with the following
-        # BrokenProcessPool error
-        bpe = BrokenProcessPool("A process in the process pool was "
-                                "terminated abruptly while the future was "
-                                "running or pending.")
+        # All pending tasks are to be marked failed with a
+        # BrokenProcessPool error, as separate instances to avoid sharing
+        # a traceback (gh-101267).
         cause_str = None
         if cause is not None:
             cause_str = ''.join(cause)
@@ -489,11 +487,15 @@ def _terminate_broken(self, cause):
                                   f"with exit code {p.exitcode}")
             if errors:
                 cause_str = "\n".join(errors)
-        if cause_str:
-            bpe.__cause__ = _RemoteTraceback(f"\n'''\n{cause_str}'''")
+        cause_tb = f"\n'''\n{cause_str}'''" if cause_str else None
 
         # Mark pending tasks as failed.
         for work_id, work_item in self.pending_work_items.items():
+            bpe = BrokenProcessPool("A process in the process pool was "
+                                    "terminated abruptly while the future was "
+                                    "running or pending.")
+            if cause_tb is not None:
+                bpe.__cause__ = _RemoteTraceback(cause_tb)
             try:
                 work_item.future.set_exception(bpe)
             except _base.InvalidStateError:

Lib/test/test_concurrent_futures/test_process_pool.py

@@ -3,6 +3,7 @@
 import sys
 import threading
 import time
+import traceback
 import unittest
 import unittest.mock
 from concurrent import futures
@@ -62,6 +63,32 @@ def test_killed_child(self):
         # Submitting other jobs fails as well.
         self.assertRaises(BrokenProcessPool, self.executor.submit, pow, 2, 8)
 
+    @warnings_helper.ignore_fork_in_thread_deprecation_warnings()
+    def test_broken_process_pool_traceback(self):
+        # When a child process is abruptly terminated, the whole pool gets
+        # "broken", and a BrokenProcessPool exception should be created
+        # for each future instead of sharing one exception among all futures.
+        event = self.create_event()
+        futures = [self.executor.submit(event.wait) for _ in range(3)]
+        p = next(iter(self.executor._processes.values()))
+        p.terminate()
+        for fut in futures:
+            # Don't use assertRaises(): it clears the traceback off exc.
+            try:
+                fut.result()
+            except BrokenProcessPool as exc:
+                tb = exc.__traceback__
+            else:
+                self.fail("BrokenProcessPool not raised")
+            count = sum(
+                1
+                for frame_summary in traceback.extract_tb(tb)
+                if frame_summary.filename == __file__
+            )
+            # This code file should appear exactly once in the traceback.
+            # A shared exception would accumulate a frame per result() call.
+            self.assertEqual(count, 1)
+
     @warnings_helper.ignore_fork_in_thread_deprecation_warnings()
     def test_map_chunksize(self):
         def bad_map():

Misc/ACKS

@@ -1763,6 +1763,7 @@ Charlie Shepherd
 Bruce Sherwood
 Gregory Shevchenko
 Hai Shi
+Daniel Shields
 Alexander Shigin
 Pete Shinners
 Michael Shiplett

Misc/NEWS.d/next/Library/2023-01-23-21-23-50.gh-issue-101267._f-cFH.rst

@@ -0,0 +1,7 @@
+When a worker process terminates unexpectedly,
+:class:`concurrent.futures.ProcessPoolExecutor` now sets a separate
+:exc:`~concurrent.futures.process.BrokenProcessPool` exception on each pending
+future instead of sharing a single instance among them all.  Sharing one
+exception produced malformed tracebacks: each
+:meth:`Future.result() <concurrent.futures.Future.result>` call re-raised the
+same object, appending another copy of the traceback to it.

Misc/NEWS.d/next/Library/2026-06-12-22-46-31.gh-issue-151403.DalZWh.rst

@@ -0,0 +1,3 @@
+Fixed a crash in :class:`subprocess.Popen` (and ``_posixsubprocess.fork_exec``)
+when an ``argv`` item's :meth:`~os.PathLike.__fspath__` concurrently mutates the
+``args`` sequence being converted.

Misc/NEWS.d/next/Library/2026-06-13-04-11-00.gh-issue-151426.f2V67e.rst

@@ -0,0 +1,4 @@
+Fix impossible stack traces (callers and callees cross called, orphans and
+incorrect lines) in the Tachyon profiler when caching frames, by snapshotting
+the stack chunks before walking the frame chain on a cache miss. Patch by
+Maurycy Pawłowski-Wieroński.

Modules/_posixsubprocess.c

@@ -1090,8 +1090,14 @@ subprocess_fork_exec_impl(PyObject *module, PyObject *process_args,
                 goto cleanup;
             }
             borrowed_arg = PySequence_Fast_GET_ITEM(fast_args, arg_num);
-            if (PyUnicode_FSConverter(borrowed_arg, &converted_arg) == 0)
+            /* borrowed_arg is only borrowed; its __fspath__() may run Python
+               that drops fast_args' last reference to it. */
+            Py_INCREF(borrowed_arg);
+            if (PyUnicode_FSConverter(borrowed_arg, &converted_arg) == 0) {
+                Py_DECREF(borrowed_arg);
                 goto cleanup;
+            }
+            Py_DECREF(borrowed_arg);
             PyTuple_SET_ITEM(converted_args, arg_num, converted_arg);
         }