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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:
 """Returns the route associated to a callsign."""

        from .. import airports

        c = requests.get(
            f"https://opensky-network.org/api/routes?callsign={callsign}"
        )
        if c.status_code == 404:
            raise ValueError("Unknown callsign")
        if c.status_code != 200:
            raise ValueError(c.content.decode())
        json = c.json()

        return tuple(airports[a] for a in json["route"])