from timeit import timeit

setup = '''
from random import random, seed
from operator import itemgetter
seed(42)    # repeatability
x = [(random(), random()) for _ in xrange(10000000)]
'''

cmptime = timeit('x.sort(cmp=lambda a,b: cmp(a[1], b[1]))', setup, number=3)
keytime = timeit('x.sort(key=itemgetter(1))', setup, number=3)

print 'time using cmp: %.6f\ntime using key: %.6f (faster by %.3fx)' % (cmptime, keytime, cmptime/keytime)