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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 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