def bigquery_serialize_date(py_date):
    """
    Convert a python date object into a serialized format that Bigquery accepts.
    Accurate to days.
    Bigguery format: 'YYYY-[M]M-[D]D'
    https://cloud.google.com/bigquery/docs/reference/standard-sql/data-types

    Args:
        py_date (datetime.date):  The date to convert.
    Returns:
        (str): The Serialized date.
    """
    return py_date.strftime('%Y-%m-%d')