def chdir(directory):
    """Remember and return current directory before calling os.chdir().
    If the current directory could not be determined, return None.
    """
    try:
        olddir = os.getcwd()
    except OSError:
        olddir = None
    os.chdir(directory)
    return olddir
Remember and return current directory before calling os.chdir().
    If the current directory could not be determined, return None.