Simple implementation of graph

simplegraph.py

class SimpleGraph(object):

    def __init__(self, edges, weights=None):
        self._edges = edges
        self._weights = weights

    def neighbors(self, id):
        return self._edges[id]

    def cost(self, start, end):
        return self._weights[(start, end)]

    @property
    def nodes(self):
        return self._edges.keys()