I have a function that resembles the one below. I'm not sure how to use the os module to get back to my original working directory at the conclusion of the jar's execution.
def run():
owd = os.getcwd()
#first change dir to build_dir path
os.chdir(testDir)
#run jar from test directory
os.system(cmd)
#change dir back to original working directory (owd)
note: I think my code formatting is off - not sure why. My apologies in advance
A context manager is a very appropriate tool for this job:
from contextlib import contextmanager
import os
@contextmanager
def cwd(path):
oldpwd = os.getcwd()
os.chdir(path)
try:
yield
finally:
os.chdir(oldpwd)
...used as:
os.chdir('/tmp') # for testing purposes, be in a known directory
print(f'before context manager: {os.getcwd()}')
with cwd('/'):
# code inside this block, and only inside this block, is in the new directory
print(f'inside context manager: {os.getcwd()}')
print(f'after context manager: {os.getcwd()}')
...which will yield something like:
before context manager: /tmp
inside context manager: /
after context manager: /tmp
This is actually superior to the cd - shell builtin, inasmuch as it also takes care of changing directories back when a block is exited due to an exception being thrown.
For your specific use case, this would instead be:
with cwd(testDir):
os.system(cmd)
Another option to consider is using subprocess.call() instead of os.system(), which will let you specify a working directory for the command to run:
# note: better to modify this to not need shell=True if possible
subprocess.call(cmd, cwd=testDir, shell=True)
... which would prevent you from needing to change the interpreter's directory at all.
Note that now it is recommended to use subprocess.run (instead of call) but the same arguments are available, and in particular cwd: https://docs.python.org/3/library/subprocess.html#using-the-subprocess-module.
You simply need to add the line:
os.chdir(owd)
Just a note this was also answered in your other question.
The advice to use os.chdir(owd) is good. It would be wise to put the code which needs the changed directory in a try:finally block (or in python 2.6 and later, a with: block.) That reduces the risk that you will accidentally put a return in the code before the change back to the original directory.
def run():
owd = os.getcwd()
try:
#first change dir to build_dir path
os.chdir(testDir)
#run jar from test directory
os.system(cmd)
finally:
#change dir back to original working directory (owd)
os.chdir(owd)
You can now simply use contextlib.chdir from stdlib. It changes the directory when entering the block, it then restores the old directory back:
from contextlib import chdir
from os import getcwd
print(f"Before: {getcwd()}")
with chdir("/"):
print(f"inside: {getcwd()}")
print(f"after: {getcwd()}")
A context-manager is overkill for this situation (executing a system command). The best solution is to use the subprocess module instead (Python 2.4 onwards) and the run or popen methods with the cwd argument.
So, your code can be replaced with:
def run():
#run jar from test directory
subprocess.run(cmd, cwd=testDir)
See https://bugs.python.org/issue25625 and https://docs.python.org/3/library/subprocess.html#subprocess-replacements.
os.chdir(owd) should do the trick (like you've done when changing to testDir)
Python is case sensitive so when typing the path make sure it's the same as the directory you want to set.
import os
os.getcwd()
os.chdir('C:\\')
I looked around the answers on StackOverflow and eventually decided to write my own decorator for this purpose:
from collections.abc import Callable
from functools import wraps
from typing import ParamSpec, TypeVar
T = TypeVar('T')
P = ParamSpec('P')
def enter_subdir(subdir: str) -> Callable[[Callable[P, T]], Callable[P, T]]:
"""During the execution of a function, temporarily enter a subdirectory."""
def decorator(function: Callable[P, T]) -> Callable[P, T]:
@wraps(function)
def wrapper(*args, **kwargs) -> T:
os.makedirs(subdir, exist_ok=True)
os.chdir(subdir)
result = function(*args, **kwargs)
os.chdir("..")
return result
return wrapper
return decorator
