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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_active_channels_by_year_quarter( self, channel_type, year, quarter, expires=None):
 """ Search for all active channels by year and quarter """

        if expires is None:
            # Set expires_after to midnight of current day
            expires = datetime.combine(datetime.utcnow().date(), time.min)

        return self.search_channels(
            type=channel_type, tag_year=year, tag_quarter=quarter,
            expires_after=expires.isoformat())