human
I wrote the below code

    (left, right) = bipartite_sets(G, top_nodes)
    G = nx.DiGraph(G.edges(left))
    matching = {}
    for u in G:
        for v in G[u]:
            if (v not in matching):
                matching[v] = u
                break
    while True:
        preds = {}
        unmatched = []
        pred = {u: unmatched for u in G}
        for v in matching:
            del pred[matching[v]]
        layer = list(pred)
        while (layer and (not unmatched)):
            newLayer = {}
            for u in layer:
                for v in G[u]:
                    if (v not in preds):
                        newLayer.setdefault(v, []).append(u)
            layer = []
            for v in newLayer:
                preds[v] = newLayer[v]
                if (v in matching):
                    layer.append(matching[v])
                    pred[matching[v]] = v
                else:
                    unmatched.append(v)
        if (not unmatched):
            unlayered = {}
            for u in G:
                for v in G[u]:
                    if (v not in preds):
                        unlayered[v] = None
            for key in matching.copy():
                matching[matching[key]] = key
            return matching
        def recurse(v):
            if (v in preds):
                L = preds.pop(v)
                for u in L:
                    if (u in pred):
                        pu = pred.pop(u)
                        if ((pu is unmatched) or recurse(pu)):
                            matching[v] = u
                            return True
            return False
        for v in unmatched:
            recurse(v)

What's a good function header?
 Here's a good function header?
assistant
#Here's a good function header.

def eppstein_matching(G, top_nodes=None):