def check_data_format(data_format):
    """
    Checks if data_format specified (if it is at all) is either None, 'Csv', or 'pandas'.
    It exits program with error message if input isn't good.

    :param data_format: data_format provided 

    :return: Boolean - True if good
    """
    if not data_format or data_format.lower() not in ['csv', 'pandas']:
        raise ValueError(
            """{} is an unspecified data format. The two options are Csv and Pandas (Csv is default)
"""
            .format(data_format))
