def docker_path(filepath, work_dir=None):
    """
    Given a path, return that files path inside the docker mount directory (/data).

    :param str filepath: The path to a file
    :param str work_dir: The part of the path to replace with /data
    :return: The docker-friendly path for `filepath`
    :rtype: str
    """
    if work_dir:
        return re.sub(work_dir, '/data', filepath)

    else:
        return os.path.join('/data', os.path.basename(filepath))