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Solve the following python programming problem given the following code:
def bandwidth_usage(instance_ref, audit_start, ignore_missing_network_data = True) : 
    'Get bandwidth usage information for the instance for the
    specified audit period.
    ' 
    admin_context = nova.context.get_admin_context (read_deleted = 'yes') 
    def _get_nwinfo_old_skool() : 
        'Support for getting network info without objects.' 
        if (instance_ref.get ('info_cache') and (instance_ref ['info_cache'].get ('network_info') is not None)) : 
            cached_info = instance_ref ['info_cache'] ['network_info'] 
            if isinstance (cached_info, network_model.NetworkInfo) : 
                return cached_info 
return network_model.NetworkInfo.hydrate (cached_info) 
try : 
            return network.API ().get_instance_nw_info (admin_context, instance_ref) 
except Exception : 
            try : 
                with excutils.save_and_reraise_exception () : 
                    LOG.exception (_LE ('Failed to get nw_info'), instance = instance_ref) 
except Exception : 
                if ignore_missing_network_data : 
                    return 
raise 
if isinstance (instance_ref, obj_base.NovaObject) : 
        nw_info = instance_ref.info_cache.network_info 
        if (nw_info is None) : 
            nw_info = network_model.NetworkInfo () 
else : 
        nw_info = _get_nwinfo_old_skool () 
macs = [vif ['address'] for vif in nw_info] 
    uuids = [instance_ref ['uuid']] 
    bw_usages = objects.BandwidthUsageList.get_by_uuids (admin_context, uuids, audit_start) 
    bw = { 
        
} 
    for b in bw_usages : 
        if (b.mac in macs) : 
            label = ('net-name-not-found-%s' % b.mac) 
            for vif in nw_info : 
                if (vif ['address'] == _get_nwinfo_old_skool.mac) : 
                    label = vif ['network'] ['label'] 
                    break 
bw [label] = dict (bw_in = b.bw_in, bw_out = b.bw_out) 
return bw 

    
    

    Fix the buggy line: if (vif ['address'] == _get_nwinfo_old_skool.mac) :
assistant
#Here is Python code to fix the buggy line: if (vif ['address'] == _get_nwinfo_old_skool.

if (vif ['address'] == b.mac) :