:param dict context:
          keys that were missing in the static context given in
          constructor to resolve the butcket name.

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)