问networkx shortest_path(G[，源，目标，权重]函数的源算法

EN

def single_source_shortest_path(G,source,cutoff=None):
    level=0                  # the current level
    nextlevel={source:1}       # list of nodes to check at next level
    paths={source:[source]}  # paths dictionary  (paths to key from source)
    if cutoff==0:
        return paths
    while nextlevel:
        thislevel=nextlevel
        nextlevel={}
        for v in thislevel:
            for w in G[v]:
                if w not in paths:
                    paths[w]=paths[v]+[w]
                    nextlevel[w]=1
        level=level+1
        if (cutoff is not None and cutoff <= level):  break
    return paths

 ...
 if source is None:
        if target is None:
            if weight is None:
                paths=nx.all_pairs_shortest_path(G)
            else:
                paths=nx.all_pairs_dijkstra_path(G,weight=weight)
        else:
            raise nx.NetworkXError(\
                "Target given but no source specified.")
    else: # source specified
        if target is None:
            if weight is None:
                paths=nx.single_source_shortest_path(G,source)
            else:
                paths=nx.single_source_dijkstra_path(G,source,weight=weight)
        else:
            # shortest source-target path
            if weight is None:
                paths=nx.bidirectional_shortest_path(G,source,target)
            else:
                paths=nx.dijkstra_path(G,source,target,weight)

    return paths