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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(self, external_site: str, external_id: int):
 """ Get a kitsu mapping by external site ID :param str external_site: string representing the external site :param int external_id: ID of the entry in the external site. :return: Dictionary or None (for not found) :rtype: Dictionary or None :raises: :class:`Pymoe.errors.ServerError` """

        r = requests.get(self.apiurl + "/mappings", params={"filter[externalSite]": external_site, "filter[externalId]": external_id}, headers=self.header)

        if r.status_code != 200:
          raise ServerError

        jsd = r.json()

        if len(jsd['data']) < 1:
          return None

        r = requests.get(jsd['data'][0]['relationships']['item']['links']['related'], headers=self.header)

        if r.status_code != 200:
            return jsd
        else:
            return r.json()