def expand_buses(pins_nets_buses):
    """
    Take list of pins, nets, and buses and return a list of only pins and nets.
    """

    # This relies on the fact that a bus is an iterable of its nets,
    # and pins/nets return an iterable containing only a single pin/net.
    pins_nets = []
    for pnb in pins_nets_buses:
        pins_nets.extend(pnb)
    return pins_nets