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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 allow_address_pairs(session, network, subnet):
 """Allow several interfaces to be added and accessed from the other machines. This is particularly useful when working with virtual ips. """

    nclient = neutron.Client('2', session=session,
                             region_name=os.environ['OS_REGION_NAME'])
    ports = nclient.list_ports()
    ports_to_update = filter(
        lambda p: p['network_id'] == network['id'],
        ports['ports'])
    logger.info('[nova]: Allowing address pairs for ports %s' %
                list(map(lambda p: p['fixed_ips'], ports_to_update)))
    for port in ports_to_update:
        try:
            nclient.update_port(port['id'], {
                'port': {
                    'allowed_address_pairs': [{
                        'ip_address': subnet
                        }]
                    }
                })
        except Exception:
            # NOTE(msimonin): dhcp and router interface port
            # seems to have enabled_sec_groups = False which
            # prevent them to be updated, just throw a warning
            # a skip them
            logger.warn("Can't update port %s" % port)