AttributeError: 'str' object has no attribute 'copy'

在使用Python Networkx 中的relabel_nodes函数时，出现：

AttributeError: 'str' object has no attribute 'copy'

找了半天也没发现错误出现在哪里，通过比较发现：

如果在定义图的类型时候使用G=nx.MultiDiGraph()就会出现这个错误，改为G=nx.Graph()错误消失。

目测是relabel_nodes函数不支持MultiDiGraph。

附：

def relabel_nodes(G, mapping, copy=True):
    """Relabel the nodes of the graph G.

    Parameters
    ----------
    G : graph
       A NetworkX graph

    mapping : dictionary
       A dictionary with the old labels as keys and new labels as values.
       A partial mapping is allowed.

    copy : bool (optional, default=True)
       If True return a copy, or if False relabel the nodes in place.

    Examples
    --------
    >>> G=nx.path_graph(3)  # nodes 0-1-2
    >>> mapping={0:'a',1:'b',2:'c'}
    >>> H=nx.relabel_nodes(G,mapping)
    >>> print(sorted(H.nodes()))
    ['a', 'b', 'c']

    >>> G=nx.path_graph(26) # nodes 0..25
    >>> mapping=dict(zip(G.nodes(),"abcdefghijklmnopqrstuvwxyz"))
    >>> H=nx.relabel_nodes(G,mapping) # nodes a..z
    >>> mapping=dict(zip(G.nodes(),range(1,27)))
    >>> G1=nx.relabel_nodes(G,mapping) # nodes 1..26

    Partial in-place mapping:

    >>> G=nx.path_graph(3)  # nodes 0-1-2
    >>> mapping={0:'a',1:'b'} # 0->'a' and 1->'b'
    >>> G=nx.relabel_nodes(G,mapping, copy=False)

    print(G.nodes())
    [2, 'b', 'a']

    Mapping as function:

    >>> G=nx.path_graph(3)
    >>> def mapping(x):
    ...    return x**2
    >>> H=nx.relabel_nodes(G,mapping)
    >>> print(H.nodes())
    [0, 1, 4]

    Notes
    -----
    Only the nodes specified in the mapping will be relabeled.

    The keyword setting copy=False modifies the graph in place.
    This is not always possible if the mapping is circular.
    In that case use copy=True.

    See Also
    --------
    convert_node_labels_to_integers
    """
    # you can pass a function f(old_label)->new_label
    # but we'll just make a dictionary here regardless
    if not hasattr(mapping,"__getitem__"):
        m = dict((n, mapping(n)) for n in G)
    else:
        m = mapping
    if copy:
        return _relabel_copy(G, m)
    else:
        return _relabel_inplace(G, m)