lists.sort() with cmp

[snippsat]

itemgetter() could be faster

No,you are guessing again 
You can test,timeit work fine.
lambda is a lot faster.

# Python 3.6
import timeit

_lambda = '''\
lst = [('Tom', 'C', 10), ('Kent', 'A', 12), ('Jenny', 'B', 15)]
sorted(lst, key=lambda tup: tup[1])
'''
#--> 18.7 sec

_itemgetter = '''\
from operator import itemgetter
lst = [('Tom', 'C', 10), ('Kent', 'A', 12), ('Jenny', 'B', 15)]
sorted(lst, key=itemgetter(1))
'''
#--> 33.8 sec

print(timeit.Timer(stmt=_lambda).timeit(number=10000000))