bpo-25625: add contextlib.chdir (GH-28271)

Added non parallel-safe :func:`~contextlib.chdir` context manager to change
the current working directory and then restore it on exit. Simple wrapper
around :func:`~os.chdir`.

Signed-off-by: Filipe Laíns <lains@riseup.net>
Co-authored-by: Łukasz Langa <lukasz@langa.pl>
This commit is contained in:
Filipe Laíns 2021-10-19 23:19:27 +01:00 committed by GitHub
parent ad6d162e51
commit 3592980f91
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4 changed files with 83 additions and 3 deletions

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@ -353,6 +353,23 @@ Functions and classes provided:
.. versionadded:: 3.5
.. function:: chdir(path)
Non parallel-safe context manager to change the current working directory.
As this changes a global state, the working directory, it is not suitable
for use in most threaded or aync contexts. It is also not suitable for most
non-linear code execution, like generators, where the program execution is
temporarily relinquished -- unless explicitely desired, you should not yield
when this context manager is active.
This is a simple wrapper around :func:`~os.chdir`, it changes the current
working directory upon entering and restores the old one on exit.
This context manager is :ref:`reentrant <reentrant-cms>`.
.. versionadded:: 3.11
.. class:: ContextDecorator()
A base class that enables a context manager to also be used as a decorator.
@ -900,8 +917,8 @@ but may also be used *inside* a :keyword:`!with` statement that is already
using the same context manager.
:class:`threading.RLock` is an example of a reentrant context manager, as are
:func:`suppress` and :func:`redirect_stdout`. Here's a very simple example of
reentrant use::
:func:`suppress`, :func:`redirect_stdout`, and :func:`chdir`. Here's a very
simple example of reentrant use::
>>> from contextlib import redirect_stdout
>>> from io import StringIO

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@ -1,5 +1,6 @@
"""Utilities for with-statement contexts. See PEP 343."""
import abc
import os
import sys
import _collections_abc
from collections import deque
@ -9,7 +10,8 @@ from types import MethodType, GenericAlias
__all__ = ["asynccontextmanager", "contextmanager", "closing", "nullcontext",
"AbstractContextManager", "AbstractAsyncContextManager",
"AsyncExitStack", "ContextDecorator", "ExitStack",
"redirect_stdout", "redirect_stderr", "suppress", "aclosing"]
"redirect_stdout", "redirect_stderr", "suppress", "aclosing",
"chdir"]
class AbstractContextManager(abc.ABC):
@ -762,3 +764,18 @@ class nullcontext(AbstractContextManager, AbstractAsyncContextManager):
async def __aexit__(self, *excinfo):
pass
class chdir(AbstractContextManager):
"""Non thread-safe context manager to change the current working directory."""
def __init__(self, path):
self.path = path
self._old_cwd = []
def __enter__(self):
self._old_cwd.append(os.getcwd())
os.chdir(self.path)
def __exit__(self, *excinfo):
os.chdir(self._old_cwd.pop())

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@ -1,6 +1,7 @@
"""Unit tests for contextlib.py, and other context managers."""
import io
import os
import sys
import tempfile
import threading
@ -1114,5 +1115,47 @@ class TestSuppress(unittest.TestCase):
1/0
self.assertTrue(outer_continued)
class TestChdir(unittest.TestCase):
def test_simple(self):
old_cwd = os.getcwd()
target = os.path.join(os.path.dirname(__file__), 'data')
self.assertNotEqual(old_cwd, target)
with chdir(target):
self.assertEqual(os.getcwd(), target)
self.assertEqual(os.getcwd(), old_cwd)
def test_reentrant(self):
old_cwd = os.getcwd()
target1 = os.path.join(os.path.dirname(__file__), 'data')
target2 = os.path.join(os.path.dirname(__file__), 'ziptestdata')
self.assertNotIn(old_cwd, (target1, target2))
chdir1, chdir2 = chdir(target1), chdir(target2)
with chdir1:
self.assertEqual(os.getcwd(), target1)
with chdir2:
self.assertEqual(os.getcwd(), target2)
with chdir1:
self.assertEqual(os.getcwd(), target1)
self.assertEqual(os.getcwd(), target2)
self.assertEqual(os.getcwd(), target1)
self.assertEqual(os.getcwd(), old_cwd)
def test_exception(self):
old_cwd = os.getcwd()
target = os.path.join(os.path.dirname(__file__), 'data')
self.assertNotEqual(old_cwd, target)
try:
with chdir(target):
self.assertEqual(os.getcwd(), target)
raise RuntimeError("boom")
except RuntimeError as re:
self.assertEqual(str(re), "boom")
self.assertEqual(os.getcwd(), old_cwd)
if __name__ == "__main__":
unittest.main()

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@ -0,0 +1,3 @@
Added non parallel-safe :func:`~contextlib.chdir` context manager to change
the current working directory and then restore it on exit. Simple wrapper
around :func:`~os.chdir`.