from contextlib import contextmanager
import os

@contextmanager
def cd(newdir):
    prevdir = os.getcwd()
    os.chdir(os.path.expanduser(newdir))
    try:
        yield
    finally:
        os.chdir(prevdir)

# cd using context manager and decorator
# directory is reverted even after an exception is thrown

os.chdir('/home')

with cd('/tmp'):
    # ...
    raise Exception("There's no place like home.")
# Directory is now back to '/home'.