https://github.com/python/cpython/commit/ca66d3c40cd9ac1fb94dd7cd79ccb8fecf019527
commit: ca66d3c40cd9ac1fb94dd7cd79ccb8fecf019527
branch: main
author: Serhiy Storchaka <[email protected]>
committer: serhiy-storchaka <[email protected]>
date: 2026-02-24T13:05:06+02:00
summary:
gh-66305: Fix a hang on Windows in the tempfile module (GH-144672)
It occurred when trying to create a temporary file or subdirectory in
a non-writable directory.
files:
A Misc/NEWS.d/next/Library/2026-02-10-16-56-05.gh-issue-66305.PZ6GN8.rst
M Lib/tempfile.py
M Lib/test/test_tempfile.py
diff --git a/Lib/tempfile.py b/Lib/tempfile.py
index 2bc61662459992..6dac9ab3c41717 100644
--- a/Lib/tempfile.py
+++ b/Lib/tempfile.py
@@ -57,10 +57,11 @@
if hasattr(_os, 'O_BINARY'):
_bin_openflags |= _os.O_BINARY
-if hasattr(_os, 'TMP_MAX'):
- TMP_MAX = _os.TMP_MAX
-else:
- TMP_MAX = 10000
+# This is more than enough.
+# Each name contains over 40 random bits. Even with a million temporary
+# files, the chance of a conflict is less than 1 in a million, and with
+# 20 attempts, it is less than 1e-120.
+TMP_MAX = 20
# This variable _was_ unused for legacy reasons, see issue 10354.
# But as of 3.5 we actually use it at runtime so changing it would
@@ -196,8 +197,7 @@ def _get_default_tempdir(dirlist=None):
for dir in dirlist:
if dir != _os.curdir:
dir = _os.path.abspath(dir)
- # Try only a few names per directory.
- for seq in range(100):
+ for seq in range(TMP_MAX):
name = next(namer)
filename = _os.path.join(dir, name)
try:
@@ -213,10 +213,8 @@ def _get_default_tempdir(dirlist=None):
except FileExistsError:
pass
except PermissionError:
- # This exception is thrown when a directory with the chosen
name
- # already exists on windows.
- if (_os.name == 'nt' and _os.path.isdir(dir) and
- _os.access(dir, _os.W_OK)):
+ # See the comment in mkdtemp().
+ if _os.name == 'nt' and _os.path.isdir(dir):
continue
break # no point trying more names in this directory
except OSError:
@@ -258,10 +256,8 @@ def _mkstemp_inner(dir, pre, suf, flags, output_type):
except FileExistsError:
continue # try again
except PermissionError:
- # This exception is thrown when a directory with the chosen name
- # already exists on windows.
- if (_os.name == 'nt' and _os.path.isdir(dir) and
- _os.access(dir, _os.W_OK)):
+ # See the comment in mkdtemp().
+ if _os.name == 'nt' and _os.path.isdir(dir) and seq < TMP_MAX - 1:
continue
else:
raise
@@ -386,10 +382,14 @@ def mkdtemp(suffix=None, prefix=None, dir=None):
except FileExistsError:
continue # try again
except PermissionError:
- # This exception is thrown when a directory with the chosen name
- # already exists on windows.
- if (_os.name == 'nt' and _os.path.isdir(dir) and
- _os.access(dir, _os.W_OK)):
+ # On Posix, this exception is raised when the user has no
+ # write access to the parent directory.
+ # On Windows, it is also raised when a directory with
+ # the chosen name already exists, or if the parent directory
+ # is not a directory.
+ # We cannot distinguish between "directory-exists-error" and
+ # "access-denied-error".
+ if _os.name == 'nt' and _os.path.isdir(dir) and seq < TMP_MAX - 1:
continue
else:
raise
diff --git a/Lib/test/test_tempfile.py b/Lib/test/test_tempfile.py
index 7eec34f2f294ad..b2b5390af33b00 100644
--- a/Lib/test/test_tempfile.py
+++ b/Lib/test/test_tempfile.py
@@ -330,17 +330,36 @@ def _mock_candidate_names(*names):
class TestBadTempdir:
def test_read_only_directory(self):
with _inside_empty_temp_dir():
- oldmode = mode = os.stat(tempfile.tempdir).st_mode
- mode &= ~(stat.S_IWUSR | stat.S_IWGRP | stat.S_IWOTH)
- os.chmod(tempfile.tempdir, mode)
+ probe = os.path.join(tempfile.tempdir, 'probe')
+ if os.name == 'nt':
+ cmd = ['icacls', tempfile.tempdir, '/deny', 'Everyone:(W)']
+ stdout = None if support.verbose > 1 else subprocess.DEVNULL
+ subprocess.run(cmd, check=True, stdout=stdout)
+ else:
+ oldmode = mode = os.stat(tempfile.tempdir).st_mode
+ mode &= ~(stat.S_IWUSR | stat.S_IWGRP | stat.S_IWOTH)
+ mode = stat.S_IREAD
+ os.chmod(tempfile.tempdir, mode)
try:
- if os.access(tempfile.tempdir, os.W_OK):
+ # Check that the directory is read-only.
+ try:
+ os.mkdir(probe)
+ except PermissionError:
+ pass
+ else:
+ os.rmdir(probe)
self.skipTest("can't set the directory read-only")
+ # gh-66305: Now it takes a split second, but previously
+ # it took about 10 days on Windows.
with self.assertRaises(PermissionError):
self.make_temp()
- self.assertEqual(os.listdir(tempfile.tempdir), [])
finally:
- os.chmod(tempfile.tempdir, oldmode)
+ if os.name == 'nt':
+ cmd = ['icacls', tempfile.tempdir, '/grant:r',
'Everyone:(M)']
+ subprocess.run(cmd, check=True, stdout=stdout)
+ else:
+ os.chmod(tempfile.tempdir, oldmode)
+ self.assertEqual(os.listdir(tempfile.tempdir), [])
def test_nonexisting_directory(self):
with _inside_empty_temp_dir():
diff --git
a/Misc/NEWS.d/next/Library/2026-02-10-16-56-05.gh-issue-66305.PZ6GN8.rst
b/Misc/NEWS.d/next/Library/2026-02-10-16-56-05.gh-issue-66305.PZ6GN8.rst
new file mode 100644
index 00000000000000..276711e6ba3900
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-02-10-16-56-05.gh-issue-66305.PZ6GN8.rst
@@ -0,0 +1,3 @@
+Fixed a hang on Windows in the :mod:`tempfile` module when
+trying to create a temporary file or subdirectory in a non-writable
+directory.
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