eruptions={}
num_eruptions = 0
for year in list_of_years:
    num_eruptions += eruptions.get(year,-1)
    
    
    if year in eruptions:
        num_eruptions += eruptions[year]
    else:
        num_eruptions -= 1
        
dict_name={}
dict_keys= dict_name.keys()
#dict_values = dict_name.values()

dict_keys.sort()

for key in dict_keys:
    #ordered loop
    dict_name[key]
    
    
phone_book={}
reverse_phone_book= {}

for key in reverse_phone_book:
    if reverse_phone_book[key] in phone_book:
        phone_book[reverse_phone_book[key]]= phone_book[reverse_phone_book[key]].append(key)
    else:
        phone_book[reverse_phone_book[key]]= [key]