http://stackoverflow.com/questions/34455594/why-is-sorting-a-python-list-of-tuples-faster-when-i-explicitly-provide-the-key

timeit_key_tuple_sorting.py

import timeit

repeat = 7
numbers = 1000

# repeat = numbers = 1 # uncomment to count cmp and equal calls

def time(statement, _setup=None):
    print min(
        timeit.Timer(statement, setup=_setup or setup).repeat(repeat, numbers))

imports = """
import random
import string
from operator import itemgetter

random.seed('slartibartfast')
d={}"""

print "***** STRINGS"

setup = imports + """
for i in range(1000):
    d[''.join(random.choice(string.ascii_uppercase) for _ in range(16))] = 0
"""
time('for k,v in sorted(d.iteritems()): pass')
time('for k,v in sorted(d.iteritems(),key=lambda x: x[0]): pass')
time('for k,v in sorted(d.iteritems(),key=itemgetter(0)): pass')


print "***** INTS"
setup = imports + """
for i in range(1000):
    d[random.randint(0, 1000)] = 0
"""
time('for k,v in sorted(d.iteritems()): pass')
time('for k,v in sorted(d.iteritems(), key=lambda x: x[0]): pass')
time('for k,v in sorted(d.iteritems(), key=itemgetter(0)): pass')


print "***** OBJECTS"

# repeat = numbers = 1 # uncomment to count cmp and equal calls
setup = imports + """

class A(object):
    eq_calls = 0
    cmp_calls = 0
    def __init__(self):
        self.s = ''.join(random.choice(string.ascii_uppercase) for _ in
              range(16))
    def __hash__(self): return hash(self.s)
    def __eq__(self, other):
        # self.__class__.eq_calls += 1
        return self.s == other.s
    def __ne__(self, other): return self.s != other.s
    def __cmp__(self, other):
        # self.__class__.cmp_calls += 1
        return cmp(self.s ,other.s)

for i in range(1000):
    d[A()] = 0
"""
time("""for k,v in sorted(d.iteritems()): pass
# print A.eq_calls
# print A.cmp_calls""")
time("""for k,v in sorted(d.iteritems(),key=lambda x: x[0]): pass
# print A.eq_calls
# print A.cmp_calls""")
time('for k,v in sorted(d.iteritems(),key=itemgetter(0)): pass')


print "***** BONUS range vs xrange and inlining length"

time('for _ in range(len(li)): pass', _setup="li=[x for x in xrange(100000)]")
time("""k=len(li)
for _ in range(k): pass""", _setup="li=[x for x in xrange(100000)]")

time('for _ in xrange(len(li)): pass', _setup="li=[x for x in xrange(100000)]")
time("""k=len(li)
for _ in xrange(k): pass""", _setup="li=[x for x in xrange(100000)]")