docs: def get(self, list_id=None, email_address=None, include_tracking_preference=False):
          """Gets a subscriber by list ID and email address."""
          params = {
              "email": email_address or self.email_address,
              "includetrackingpreference": include_tracking_preference,
          }
          response = self._get("/subscribers/%s.json" %
                               (list_id or self.list_id), params=params)
          return json_to_py(response)