docs: def uri(self, context=None):
          """
          :param dict context:
            keys that were missing in the static context given in
            constructor to resolve the butcket name.
          """
          if context is None:
              context = self.context
          else:
              ctx = copy.deepcopy(self.context)
              ctx.update(context)
              context = ctx
          return self.uri_format.format(**context)