def get_sink_nodes(net):
    """
    Get all the sinks in the network.

    out_degree_iter is the number of edges pointing out of the node
    http://networkx.lanl.gov/reference/generated/networkx.DiGraph.out_degree_iter.html

    Args:
        net (object): a networkx network

    Returns:
        sinks (list): a list of sink nodes [(0,1), (1,0)]
    """
    sinks = [node for node, degree in net.out_degree() if degree == 0]
    return sinks