docs: def get_roles(self):
          """Get the roles associated with the hosts.
  
          Returns
              dict of role -> [host]
          """
  
          machines = self.c_resources["machines"]
          result = {}
          for desc in machines:
              roles = utils.get_roles_as_list(desc)
              hosts = self._denormalize(desc)
              for role in roles:
                  result.setdefault(role, [])
                  result[role].extend(hosts)
          return result