Merge branch 'main' into traceback-timestamps

Resolved conflicts in sysmodule.c (keep 3.13 in comment) and test_sys.py
(adopt main's split of indexable vs name-only sys.flags attributes,
add traceback_timestamps to the name-only section).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: gpshead

Doc/library/stdtypes.rst

@@ -3514,6 +3514,11 @@ The representation of bytearray objects uses the bytes literal format
 ``bytearray([46, 46, 46])``.  You can always convert a bytearray object into
 a list of integers using ``list(b)``.
 
+.. seealso::
+
+   For detailed information on thread-safety guarantees for :class:`bytearray`
+   objects, see :ref:`thread-safety-bytearray`.
+
 
 .. _bytes-methods:
 

Doc/library/threadsafety.rst

@@ -447,3 +447,104 @@ atomic:
 
 Consider external synchronization when sharing :class:`set` instances
 across threads.  See :ref:`freethreading-python-howto` for more information.
+
+
+.. _thread-safety-bytearray:
+
+Thread safety for bytearray objects
+===================================
+
+   The :func:`len` function is lock-free and :term:`atomic <atomic operation>`.
+
+   Concatenation and comparisons use the buffer protocol, which prevents
+   resizing but does not hold the per-object lock. These operations may
+   observe intermediate states from concurrent modifications:
+
+   .. code-block::
+      :class: maybe
+
+      ba + other    # may observe concurrent writes
+      ba == other   # may observe concurrent writes
+      ba < other    # may observe concurrent writes
+
+   All other operations from here on hold the per-object lock.
+
+   Reading a single element or slice is safe to call from multiple threads:
+
+   .. code-block::
+      :class: good
+
+      ba[i]        # bytearray.__getitem__
+      ba[i:j]      # slice
+
+   The following operations are safe to call from multiple threads and will
+   not corrupt the bytearray:
+
+   .. code-block::
+      :class: good
+
+      ba[i] = x         # write single byte
+      ba[i:j] = values  # write slice
+      ba.append(x)      # append single byte
+      ba.extend(other)  # extend with iterable
+      ba.insert(i, x)   # insert single byte
+      ba.pop()          # remove and return last byte
+      ba.pop(i)         # remove and return byte at index
+      ba.remove(x)      # remove first occurrence
+      ba.reverse()      # reverse in place
+      ba.clear()        # remove all bytes
+
+   Slice assignment locks both objects when *values* is a :class:`bytearray`:
+
+   .. code-block::
+      :class: good
+
+      ba[i:j] = other_bytearray  # both locked
+
+   The following operations return new objects and hold the per-object lock
+   for the duration:
+
+   .. code-block::
+      :class: good
+
+      ba.copy()     # returns a shallow copy
+      ba * n        # repeat into new bytearray
+
+   The membership test holds the lock for its duration:
+
+   .. code-block::
+      :class: good
+
+      x in ba       # bytearray.__contains__
+
+   All other bytearray methods (such as :meth:`~bytearray.find`,
+   :meth:`~bytearray.replace`, :meth:`~bytearray.split`,
+   :meth:`~bytearray.decode`, etc.) hold the per-object lock for their
+   duration.
+
+   Operations that involve multiple accesses, as well as iteration, are never
+   atomic:
+
+   .. code-block::
+      :class: bad
+
+      # NOT atomic: check-then-act
+      if x in ba:
+          ba.remove(x)
+
+      # NOT thread-safe: iteration while modifying
+      for byte in ba:
+          process(byte)  # another thread may modify ba
+
+   To safely iterate over a bytearray that may be modified by another
+   thread, iterate over a copy:
+
+   .. code-block::
+      :class: good
+
+      # Make a copy to iterate safely
+      for byte in ba.copy():
+          process(byte)
+
+   Consider external synchronization when sharing :class:`bytearray` instances
+   across threads.  See :ref:`freethreading-python-howto` for more information.

Lib/base64.py

@@ -100,7 +100,13 @@ def b64decode(s, altchars=None, validate=_NOT_SPECIFIED, *, ignorechars=_NOT_SPE
                     break
             s = s.translate(bytes.maketrans(altchars, b'+/'))
         else:
-            trans = bytes.maketrans(b'+/' + altchars, altchars + b'+/')
+            trans_in = set(b'+/') - set(altchars)
+            if len(trans_in) == 2:
+                # we can't use the reqult of unordered sets here
+                trans = bytes.maketrans(altchars + b'+/', b'+/' + altchars)
+            else:
+                trans = bytes.maketrans(altchars + bytes(trans_in),
+                                        b'+/' + bytes(set(altchars) - set(b'+/')))
             s = s.translate(trans)
             ignorechars = ignorechars.translate(trans)
     if ignorechars is _NOT_SPECIFIED:

Lib/test/libregrtest/utils.py

@@ -150,7 +150,7 @@ def setup_unraisable_hook() -> None:
     sys.unraisablehook = regrtest_unraisable_hook
 
 
-orig_threading_excepthook: Callable[..., None] | None = None
+orig_threading_excepthook: Callable[..., object] | None = None
 
 
 def regrtest_threading_excepthook(args) -> None:

Lib/test/test_base64.py

@@ -293,6 +293,13 @@ def test_b64decode_altchars(self):
             eq(base64.b64decode(data_str, altchars=altchars_str), res)
             eq(base64.b64decode(data, altchars=altchars, ignorechars=b'\n'), res)
 
+        eq(base64.b64decode(b'/----', altchars=b'-+', ignorechars=b'/'), b'\xfb\xef\xbe')
+        eq(base64.b64decode(b'/----', altchars=b'+-', ignorechars=b'/'), b'\xff\xff\xff')
+        eq(base64.b64decode(b'+----', altchars=b'-/', ignorechars=b'+'), b'\xfb\xef\xbe')
+        eq(base64.b64decode(b'+----', altchars=b'/-', ignorechars=b'+'), b'\xff\xff\xff')
+        eq(base64.b64decode(b'+/+/', altchars=b'/+', ignorechars=b''), b'\xff\xef\xfe')
+        eq(base64.b64decode(b'/+/+', altchars=b'+/', ignorechars=b''), b'\xff\xef\xfe')
+
         self.assertRaises(ValueError, base64.b64decode, b'', altchars=b'+')
         self.assertRaises(ValueError, base64.b64decode, b'', altchars=b'+/-')
         self.assertRaises(ValueError, base64.b64decode, '', altchars='+')

Lib/test/test_sys.py

@@ -860,30 +860,37 @@ def test_subinterp_intern_singleton(self):
                     '''))
                 self.assertTrue(sys._is_interned(s))
 
-    def test_sys_flags(self):
+    def test_sys_flags_indexable_attributes(self):
         self.assertTrue(sys.flags)
-        attrs = ("debug",
+        # We've stopped assigning sequence indices to new sys.flags attributes:
+        # https://github.com/python/cpython/issues/122575#issuecomment-2416497086
+        indexable_attrs = ("debug",
                  "inspect", "interactive", "optimize",
                  "dont_write_bytecode", "no_user_site", "no_site",
                  "ignore_environment", "verbose", "bytes_warning", "quiet",
                  "hash_randomization", "isolated", "dev_mode", "utf8_mode",
-                 "warn_default_encoding", "safe_path", "int_max_str_digits",
-                 "lazy_imports", "traceback_timestamps")
-        for attr in attrs:
+                 "warn_default_encoding", "safe_path", "int_max_str_digits")
+        for attr_idx, attr in enumerate(indexable_attrs):
             self.assertHasAttr(sys.flags, attr)
             attr_type = bool if attr in ("dev_mode", "safe_path") else int
             attr_type = str if attr == "traceback_timestamps" else attr_type
             self.assertEqual(type(getattr(sys.flags, attr)), attr_type, attr)
+            attr_value = getattr(sys.flags, attr)
+            self.assertEqual(sys.flags[attr_idx], attr_value,
+                             msg=f"sys.flags .{attr} vs [{attr_idx}]")
         self.assertTrue(repr(sys.flags))
-        self.assertEqual(len(sys.flags), 18)  # Do not increase, see GH-122575
+        self.assertEqual(len(sys.flags), 18, msg="Do not increase, see GH-122575")
 
         self.assertIn(sys.flags.utf8_mode, {0, 1, 2})
 
-        # non-tuple sequence fields
+    def test_sys_flags_name_only_attributes(self):
+        # non-tuple sequence fields (name only sys.flags attributes)
         self.assertIsInstance(sys.flags.gil, int|type(None))
+        self.assertIsInstance(sys.flags.thread_inherit_context, int|type(None))
+        self.assertIsInstance(sys.flags.context_aware_warnings, int|type(None))
+        self.assertIsInstance(sys.flags.lazy_imports, int|type(None))
         self.assertIsInstance(sys.flags.traceback_timestamps, str)
 
-
     def assert_raise_on_new_sys_type(self, sys_attr):
         # Users are intentionally prevented from creating new instances of
         # sys.flags, sys.version_info, and sys.getwindowsversion.
@@ -1923,7 +1930,9 @@ def test_pythontypes(self):
         # - 'context_aware_warnings'
         # - 'lazy_imports'
         # - 'traceback_timestamps'
-        # It will not be necessary once GH-122575 is fixed.
+        # Not needing to increment this every time we add a new field
+        # per GH-122575 would be nice...
+        # Q: What is the actual point of this sys.flags C size derived from PyStructSequence_Field array assertion?
         non_sequence_fields = 5
         check(sys.flags, vsize('') + self.P + self.P * (non_sequence_fields + len(sys.flags)))
 

Misc/NEWS.d/next/Library/2026-03-15-10-17-51.gh-issue-145968.gZexry.rst

@@ -0,0 +1,2 @@
+Fix translation in :func:`base64.b64decode` when altchars overlaps with the
+standard ones.

Misc/NEWS.d/next/Tools-Demos/2026-03-15-11-32-35.gh-issue-145976.mqhzmB.rst

@@ -0,0 +1 @@
+Remove :file:`Misc/vgrindefs` and :file:`Misc/Porting`.

Misc/Porting

@@ -11,7 +11,6 @@ ACKS                    Acknowledgements
 HISTORY                 News from previous releases -- oldest last
 indent.pro              GNU indent profile approximating my C style
 NEWS                    News for this release (for some meaning of "this")
-Porting                 Mini-FAQ on porting to new platforms
 python-config.in        Python script template for python-config
 python.man              UNIX man page for the python interpreter
 python.pc.in            Package configuration info template for pkg-config
@@ -22,4 +21,3 @@ SpecialBuilds.txt       Describes extra symbols you can set for debug builds
 svnmap.txt              Map of old SVN revs and branches to hg changeset ids,
                         help history-digging
 valgrind-python.supp    Valgrind suppression file, see README.valgrind
-vgrindefs               Python configuration for vgrind (a generic pretty printer)