code: def node2bracket(docgraph, node_id, child_str=''):
      
      node_attrs = docgraph.node[node_id]
      if istoken(docgraph, node_id):
          pos_str = node_attrs.get(docgraph.ns+':pos', '')
          token_str = node_attrs[docgraph.ns+':token']
          return u"({pos}{space1}{token}{space2}{child})".format(
              pos=pos_str, space1=bool(pos_str)*' ', token=token_str,
              space2=bool(child_str)*' ', child=child_str)
  
      #else: node is not a token
      label_str = node_attrs.get('label', '')
      return u"({label}{space}{child})".format(
          label=label_str, space=bool(label_str and child_str)*' ',
          child=child_str)
docs: convert a docgraph node into a PTB-style string.