Sync pre-release CPython main branch from GitHub (2026-08-31)

Summary:
Imported python/cpython `3.16.0a0` from upstream rev [`b38e073`](https://www.github.com/python/cpython/commit/b38e073f1be8fe40af991c044a791cefff098f0d) (committed 2026-08-31 21:54:35+00:00).

# Commit Info

- Base: (`3.16.0a0`) - [`03503dc`](https://www.github.com/python/cpython/commit/03503dccd0aa6d8895614e80ae9c78c03c813d45) (commit date: 2026-08-30 21:43:38+00:00)
- Imported: (`3.16.0a0`) - [`b38e073`](https://www.github.com/python/cpython/commit/b38e073f1be8fe40af991c044a791cefff098f0d) (commit date: 2026-08-31 21:54:35+00:00)

# Noteworthy file changes

- Low-signal files (7 added, 1 removed) (NEWS.d, docs, .github)

Complete list of added/removed files: https://www.internalfb.com/intern/everpaste/?color=0&handle=GMDh2RyY_BolHpaIAJBFADyfsL5kbr0LAAAz

Differential Revision: D118237701

fbshipit-source-id: 87533c616a6224c5d45ee04948d79d4c06ee0258

Author: generatedunixname1734921407115435

Doc/library/ast.rst

@@ -2254,7 +2254,7 @@ and classes for traversing abstract syntax trees:
 
    In addition, if ``mode`` is ``'func_type'``, the input syntax is
    modified to correspond to :pep:`484` "signature type comments",
-   e.g. ``(str, int) -> List[str]``.
+   for example ``(str, int) -> List[str]``.
 
    Setting ``feature_version`` to a tuple ``(major, minor)`` will result in
    a "best-effort" attempt to parse using that Python version's grammar.

Lib/asyncio/taskgroups.py

@@ -239,6 +239,9 @@ def create_task(self, coro, **kwargs):
         # the current task too early. gh-128550, gh-128588
         self._tasks.add(task)
         task.add_done_callback(self._on_task_done)
+        # gh-155418: an eager task can cancel the group before joining _tasks
+        if self._aborting and not task.done():
+            task.cancel()
         try:
             return task
         finally:

Lib/enum.py

@@ -624,9 +624,13 @@ def __new__(metacls, cls, bases, classdict, *, boundary=None, _simple=False, **k
                     '__invert__'
                 ):
                 if name not in classdict:
+                    # check for mixin overrides before replacing
                     enum_method = getattr(Flag, name)
-                    setattr(enum_class, name, enum_method)
-                    classdict[name] = enum_method
+                    found_method = getattr(enum_class, name)
+                    data_type_method = getattr(member_type, name, None)
+                    if found_method in (enum_method, data_type_method):
+                        setattr(enum_class, name, enum_method)
+                        classdict[name] = enum_method
         #
         # replace any other __new__ with our own (as long as Enum is not None,
         # anyway) -- again, this is to support pickle

Lib/http/cookiejar.py

@@ -627,7 +627,7 @@ def request_host(request):
 
     """
     url = request.get_full_url()
-    host = urllib.parse.urlparse(url)[1]
+    host = urllib.parse.urlparse(url).netloc
     if host == "":
         host = request.get_header("Host", "")
 

Lib/test/libregrtest/refleak.py

@@ -1,6 +1,7 @@
 import os
 import sys
 import warnings
+from array import array
 from inspect import isabstract
 from typing import Any
 import linecache
@@ -100,24 +101,20 @@ def runtest_refleak(test_name, test_func,
     for obj in ByteString.__subclasses__() + [ByteString]:  # type: ignore[attr-defined]
         abcs[obj] = _get_dump(obj)[0]
 
-    # bpo-31217: Integer pool to get a single integer object for the same
-    # value. The pool is used to prevent false alarm when checking for memory
-    # block leaks. Fill the pool with values in -1000..1000 which are the most
-    # common (reference, memory block, file descriptor) differences.
-    int_pool = {value: value for value in range(-1000, 1000)}
-    def get_pooled_int(value):
-        return int_pool.setdefault(value, value)
-
     warmups = hunt_refleak.warmups
     runs = hunt_refleak.runs
     filename = hunt_refleak.filename
     repcount = warmups + runs
 
-    # Pre-allocate to ensure that the loop doesn't allocate anything new
+    # Pre-allocate to ensure that the loop doesn't allocate anything new.
+    # Store the deltas as raw values in arrays rather than as int objects in
+    # lists: each unique delta stored as an object would live until the end of
+    # the loop and show up in the following repetition's reference and memory
+    # block deltas (gh-75400, gh-155981).
     rep_range = list(range(repcount))
-    rc_deltas = [0] * repcount
-    alloc_deltas = [0] * repcount
-    fd_deltas = [0] * repcount
+    rc_deltas = array('q', [0]) * repcount
+    alloc_deltas = array('q', [0]) * repcount
+    fd_deltas = array('q', [0]) * repcount
     getallocatedblocks = sys.getallocatedblocks
     gettotalrefcount = sys.gettotalrefcount
     getunicodeinternedsize = sys.getunicodeinternedsize
@@ -161,12 +158,11 @@ def get_pooled_int(value):
         rc_after = gettotalrefcount()
         fd_after = fd_count()
 
-        rc_deltas[i] = get_pooled_int(rc_after - rc_before)
-        alloc_deltas[i] = get_pooled_int(alloc_after - alloc_before)
-        fd_deltas[i] = get_pooled_int(fd_after - fd_before)
+        rc_deltas[i] = rc_after - rc_before
+        alloc_deltas[i] = alloc_after - alloc_before
+        fd_deltas[i] = fd_after - fd_before
 
         if not quiet:
-            # use max, not sum, so total_leaks is one of the pooled ints
             total_leaks = max(rc_deltas[i], alloc_deltas[i], fd_deltas[i])
             if total_leaks <= 0:
                 symbol = '.'
@@ -212,13 +208,13 @@ def check_fd_deltas(deltas):
         return any(deltas)
 
     failed = False
-    for deltas, item_name, checker in [
+    for raw_deltas, item_name, checker in [
         (rc_deltas, 'references', check_rc_deltas),
         (alloc_deltas, 'memory blocks', check_rc_deltas),
         (fd_deltas, 'file descriptors', check_fd_deltas)
     ]:
-        # ignore warmup runs
-        deltas = deltas[warmups:]
+        # ignore warmup runs; convert to a list for reporting
+        deltas = list(raw_deltas[warmups:])
         failing = checker(deltas)
         suspicious = any(deltas)
         if failing or suspicious:

Lib/test/ssl_servers.py

@@ -61,7 +61,7 @@ def translate_path(self, path):
 
         """
         # abandon query parameters
-        path = urllib.parse.urlparse(path)[2]
+        path = urllib.parse.urlparse(path).path
         path = os.path.normpath(urllib.parse.unquote(path))
         words = path.split('/')
         words = filter(None, words)

Lib/test/support/__init__.py

@@ -868,7 +868,7 @@ def open_urlresource(url, *args, **kw):
 
     check = kw.pop('check', None)
 
-    filename = urllib.parse.urlparse(url)[2].split('/')[-1] # '/': it's URL!
+    filename = urllib.parse.urlparse(url).path.split('/')[-1] # '/': it's URL!
 
     fn = os.path.join(TEST_DATA_DIR, filename)
 

Lib/test/support/os_helper.py

@@ -434,7 +434,10 @@ def _rmtree_inner(path):
                           file=sys.__stderr__)
                     mode = 0
                 if stat.S_ISDIR(mode):
-                    _waitfor(_rmtree_inner, fullname, waitall=True)
+                    # Do not follow junctions, which os.lstat() reports
+                    # as directories.
+                    if not os.path.isjunction(fullname):
+                        _waitfor(_rmtree_inner, fullname, waitall=True)
                     _force_run(fullname, os.rmdir, fullname)
                 else:
                     _force_run(fullname, os.unlink, fullname)

Lib/test/test_ast/test_ast.py

@@ -162,6 +162,15 @@ def test_parse_invalid_ast(self):
             self.assertRaises(TypeError, ast.parse, ast.Constant(42),
                               optimize=optval)
 
+    def test_parse_ast_func_type(self):
+        # see gh-156689
+        tree = ast.parse('(int, str) -> bool', mode='func_type')
+        self.assertEqual(ast.dump(ast.parse(tree, mode='func_type')),
+                         ast.dump(tree))
+        self.assertRaises(TypeError, ast.parse, ast.Constant(42),
+                          mode='func_type')
+        self.assertRaises(TypeError, ast.parse, tree, mode='exec')
+
     def test_optimization_levels__debug__(self):
         cases = [(-1, '__debug__'), (0, '__debug__'), (1, False), (2, False)]
         for (optval, expected) in cases:

Lib/test/test_asyncio/test_taskgroups.py

@@ -1187,6 +1187,17 @@ async def test_taskgroup_cancel_before_create_task(self):
             with self.assertRaises(RuntimeError):
                 tg.create_task(asyncio.sleep(1))
 
+    async def test_taskgroup_cancel_from_child_before_first_suspension(self):
+        # gh-155418: an eager task can cancel the group before joining _tasks
+        async def child(tg):
+            tg.cancel()
+            await asyncio.sleep(10)
+            self.fail("the child was not cancelled")
+
+        async with asyncio.TaskGroup() as tg:
+            task = tg.create_task(child(tg))
+        self.assertTrue(task.cancelled())
+
     async def test_taskgroup_cancel_keeps_outer_cancellation(self):
         # gh-155433: any cancellation from outside the group must propagate.
         async def child():