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Commit c48c021

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moreatimoreati
committed
Ignore PermissionError when checking cwd during import
On macOS `getcwd(3)` can return EACCES if a path component isn't readable, resulting in PermissionError. `PathFinder.find_spec()` now catches these and ignores them - the same treatment as a missing/deleted cwd. Introduces 2 new `test.support.os_helper` context managers - `save_mode(path, ...)` - restores the mode of a path on exit - `save_cwd(...)` - restores the current directory on exit Unlike `change_cwd(path)` (which always performs a `chdir(path)`), `save_cwd()` allows the code inside the `with` block to control this. The new context manager just restores the original working directory afterward. This is allows finer control of exception handling and robust environment restoration across platforms in `FinderTests.test_permission_error_cwd()`.
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‎Doc/reference/import.rst

Copy file name to clipboardExpand all lines: Doc/reference/import.rst
+4-4Lines changed: 4 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -871,10 +871,10 @@ module.
871871

872872
The current working directory -- denoted by an empty string -- is handled
873873
slightly differently from other entries on :data:`sys.path`. First, if the
874-
current working directory is found to not exist, no value is stored in
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:data:`sys.path_importer_cache`. Second, the value for the current working
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directory is looked up fresh for each module lookup. Third, the path used for
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:data:`sys.path_importer_cache` and returned by
874+
current working directory cannot be determined or is found to not exist, no
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value is stored in :data:`sys.path_importer_cache`. Second, the value for the
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current working directory is looked up fresh for each module lookup. Third,
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the path used for :data:`sys.path_importer_cache` and returned by
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:meth:`importlib.machinery.PathFinder.find_spec` will be the actual current
879879
working directory and not the empty string.
880880

‎Lib/importlib/_bootstrap_external.py

Copy file name to clipboardExpand all lines: Lib/importlib/_bootstrap_external.py
+1-1Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1506,7 +1506,7 @@ def _path_importer_cache(cls, path):
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if path == '':
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try:
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path = _os.getcwd()
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except FileNotFoundError:
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except (FileNotFoundError, PermissionError):
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# Don't cache the failure as the cwd can easily change to
15111511
# a valid directory later on.
15121512
return None

‎Lib/test/support/os_helper.py

Copy file name to clipboardExpand all lines: Lib/test/support/os_helper.py
+55-1Lines changed: 55 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -294,6 +294,33 @@ def skip_unless_working_chmod(test):
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return test if ok else unittest.skip(msg)(test)
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@contextlib.contextmanager
298+
def save_mode(path, *, quiet=False):
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"""Context manager that restores the mode (permissions) of path on exit.
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Arguments:
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path: Path of the file to restore mode of.
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quiet: if False (the default), the context manager raises an exception
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on error. Otherwise, it issues only a warning and keeps the current
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working directory the same.
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"""
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saved_mode = os.stat(path)
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try:
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yield
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finally:
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try:
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os.chmod(path, saved_mode.st_mode)
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except OSError as exc:
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if not quiet:
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raise
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warnings.warn(f'tests may fail, unable to restore the mode of '
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f'{path!r} to {saved_mode.st_mode}: {exc}',
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RuntimeWarning, stacklevel=3)
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# Check whether the current effective user has the capability to override
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# DAC (discretionary access control). Typically user root is able to
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# bypass file read, write, and execute permission checks. The capability
@@ -508,9 +535,36 @@ def temp_dir(path=None, quiet=False):
508535
rmtree(path)
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@contextlib.contextmanager
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def save_cwd(*, quiet=False):
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"""Return a context manager that restores the current working directory on
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exit.
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Arguments:
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quiet: if False (the default), the context manager raises an exception
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on error. Otherwise, it issues only a warning and keeps the current
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working directory the same.
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"""
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saved_dir = os.getcwd()
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try:
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yield
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finally:
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try:
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os.chdir(saved_dir)
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except OSError as exc:
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if not quiet:
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raise
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warnings.warn(f'tests may fail, unable to restore the current '
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f'working directory to {saved_dir!r}: {exc}',
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RuntimeWarning, stacklevel=3)
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@contextlib.contextmanager
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def change_cwd(path, quiet=False):
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"""Return a context manager that changes the current working directory.
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"""Return a context manager that changes the current working directory on
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entry, and restores it on exit.
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515569
Arguments:
516570

‎Lib/test/test_importlib/import_/test_path.py

Copy file name to clipboardExpand all lines: Lib/test/test_importlib/import_/test_path.py
+20Lines changed: 20 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1,3 +1,4 @@
1+
from test.support import os_helper
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from test.test_importlib import util
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importlib = util.import_importlib('importlib')
@@ -153,6 +154,25 @@ def test_deleted_cwd(self):
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# Do not want FileNotFoundError raised.
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self.assertIsNone(self.machinery.PathFinder.find_spec('whatever'))
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157+
@os_helper.skip_unless_working_chmod
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def test_permission_error_cwd(self):
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# gh-115911
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with (
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os_helper.temp_dir() as new_dir,
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os_helper.save_mode(new_dir),
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os_helper.save_cwd(),
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util.import_state(path=['']),
165+
):
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os.chdir(new_dir)
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try:
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os.chmod(new_dir, 0o000)
169+
except OSError:
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self.skipTest("platform does not allow "
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"changing mode of the cwd")
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# Do not want PermissionError raised.
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self.assertIsNone(self.machinery.PathFinder.find_spec('whatever'))
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156176
def test_invalidate_caches_finders(self):
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# Finders with an invalidate_caches() method have it called.
158178
class FakeFinder:

‎Misc/NEWS.d/next/Core and Builtins/2024-02-29-16-55-52.gh-issue-115911.Vnkue_.rst

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+3Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,3 @@
1+
If the current working directory cannot be determined due to permissions,
2+
then import will no longer raise :exc:`PermissionError`. Patch by Alex
3+
Willmer.

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