def METHOD_NAME(*filenames):
    """
    Detects if the data preparation has been already done.
    If the preparation has been done, we can skip it.
    Returns
    -------
    bool
        if True, the preparation phase can be skipped.
        if False, it must be done.
    """
    for filename in filenames:
        if not os.path.isfile(filename):
            return False
    return True