code: def set_config(self, env, conf, version):
          
  
          if not isinstance(conf, collections.Mapping):
              raise ValueError("conf must be a collections.Mapping")
  
          self._set(
              self._get_env_path(env),
              conf,
              version
          )
          path = self._get_env_path(env)
          """Update env's children with new config."""
          for child in zkutil.walk(self.zk, path):
              self._update_view(Env(child[len(self.conf_path)+1:]))
docs: Set conf to env under service.
  
          pass None to env for root.