class VertexAccumulator:
    # use this class when you can't come up with a good deterministic numbering scheme for your vertices.

    def __init__(self):
        self.verts_ = []
        self.vertIdxs = {}

    def keyFor(v):
        return "%f,%f,%f"%(v[0], v[1], v[2])

    def idxFor(self, v):
        key = VertexAccumulator.keyFor(v)
        rval = self.vertIdxs.get(key)
        if None==rval:
            rval = len(self.verts_)
            self.vertIdxs[key] = rval
            self.verts_.append(v)
        return rval

    def verts(self):
        return self.verts_