def get_time_period(period_name):
    """
        Given a time period name, fetch the hydra-compatible time
        abbreviation.
    """
    time_abbreviation = time_map.get(period_name.lower())

    if time_abbreviation is None:
        raise Exception("Symbol %s not recognised as a time period"%period_name)

    return time_abbreviation
Given a time period name, fetch the hydra-compatible time
        abbreviation.