from datetime import datetime


def parse_date_YYYY_MM_DD(datestring):
    """Converts YYYY-MM-DD string into date object
    
    Args:
        datestring (str): 'YYYY-MM-DD'
    
    Returns:
        datetime.date: date represented by datestring
    
    Raises:
        ValueError: Raised if supplied string doesn't match format YYYY-MM-DD
    """

    date_fmt_str = '%Y-%m-%d'
    return_date = datetime.strptime(datestring, date_fmt_str).date()
    return return_date