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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_swell_url(self, swell_type):
 """Get swell arrow url."""

        if swell_type not in SWELL_TYPES:
            raise ValueError('Invalid swell type: {}'.format(swell_type))
        key = "swell_components_{}_direction".format(swell_type)
        swell_direction = self.f_d.get(key)
        if swell_direction is not None:
            rounded = int(5 * round(float(swell_direction)/5))
            return SWELL_ARROW_URL.format(rounded)