This will return the md5 of the file in sub_string
    :param sub_string: str of the path or relative path to a file
    :return: str

def _md5_of_file(sub_string):
    """
        This will return the md5 of the file in sub_string
    :param sub_string: str of the path or relative path to a file
    :return: str
    """
    md5 = hashlib.md5()
    file_path = sub_string
    if not os.path.exists(file_path):
        file_path = os.path.join(os.environ['CAFE_DATA_DIR_PATH'], file_path)
    if not os.path.exists(file_path):
        file_path = file_path.replace(' ', '_')
    assert (os.path.exists(file_path)), "File %s doesn't exist" % file_path
    with open(file_path, 'rb') as f:
        for chunk in iter(lambda: f.read(8192), b''):
            md5.update(chunk)
    return md5.hexdigest()