def file_mtime(file_path):
    """
    Returns the file modified time. This is with regards to the last
    modification the file has had in the droopescan repo, rather than actual
    file modification time in the filesystem.
    @param file_path: file path relative to the executable.
    @return datetime.datetime object.
    """
    if not os.path.isfile(file_path):
        raise IOError('File "%s" does not exist.' % file_path)

    ut = subprocess.check_output(['git', 'log', '-1', '--format=%ct',
        file_path]).strip()

    return datetime.fromtimestamp(int(ut))