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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def delete_vpcid_for_switch(vpc_id, switch_ip):
 """Removes unused vpcid for a switch. :param vpc_id: vpc id to remove :param switch_ip: ip address of the switch """


    LOG.debug("delete_vpcid_for_switch called")
    session = bc.get_writer_session()

    vpc = _lookup_one_vpc_allocs(vpc_id=vpc_id,
                                 switch_ip=switch_ip,
                                 active=False)
    session.delete(vpc)
    session.flush()