python ipycytoscape通过id访问节点

假设我有一个ipycytoscape图，如下所示：

railnet= '''{
    "nodes": [
        {"data": { "id": "BER", "label":"HBf BER", "classes":"east"}},
        {"data": { "id": "MUN", "label":"HBf MUN", "classes":"west"}},
        {"data": { "id": "FRA", "label":"HBf FRA", "classes":"west"}}
        ],
    "edges": [
        {"data": { "id": "line1", "source": "BER", "target": "MUN","label":"200km/h"}},
        {"data": { "id": "line2", "source": "MUN", "target": "FRA","label":"200km/h"}},
        {"data": { "id": "line3", "source": "FRA", "target": "BER","label":"250km/h" }}           
    ]
  }'''

railnetJSON = json.loads(railnet)
ipycytoscape_obj3 = ipycytoscape.CytoscapeWidget()
ipycytoscape_obj3.graph.add_graph_from_json(railnetJSON, directed=False) # I am telling I dont want directions
ipycytoscape_obj3

如何轻松访问id为的节点

这不起作用：

ipycytoscape_obj3.graph.nodes['BER']. # --> wrong