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Not quite sure if it is implemented already. However, it is not hard to implement your own. Here is one possible way of implementing it, however there might still be room to improve on performance.

def interval(g,u,v):
    duv = g.shortest_path_length(u,v)
    interval = []
    for w in g:
        if g.shortest_path_length(u,w) + g.shortest_path_length(w,v) == duv:
            interval.append(w)
    return interval

It shouldn't be hard to extend the implementation to compute the intervals between any pair of vertices. One way to achieve it would be:

intervals = {(u,v):interval(g,u,v) for u in g for v in g}