list_of_cities_for_airport=data.groupby([pd.cut(data['airports_nearest'],np.arange(0,85001,1000))])['locality_name']
list_of_cities_for_airport = list_of_cities_for_airport.apply(pd.Series.mode)
#список для заполнения

def fillnawithmode(row):
    locality= row['locality_name']
    nearest_airport = row['airports_nearest']

    for i in range(0, len(list_of_cities_for_airport)):
        if nearest_airport in list_of_cities_for_airport.index[i][0]:
            return list_of_cities_for_airport[i]
    return locality

data['locality_name_test']=data.apply(fillnawithmode, axis = 1)