gistfile1.py

import os


class DirectoryScope(object):
    
    def __init__(self, new_directory):
        self.old_directory =  os.path.abspath(os.getcwd())
        self.new_directory = os.path.abspath(new_directory)

    def __enter__(self):
        return os.chdir(self.new_directory)

    def __exit__(self, exc_type, exc_val, exc_tb ):
        os.chdir(self.old_directory)
        return exc_type is None

os.chdir('/var/')
print os.getcwd()
with DirectoryScope('/etc/'):
    print os.getcwd()
print os.getcwd()