bench.py

from __future__ import print_function
import json


bdata = b'{"foo0": "bar0","foo1": "bar1","foo2": "bar2","foo3": "bar3","foo4": "bar4","foo5": "bar5","foo6": "bar6"}'       
udata = u'{"foo0": "bar0","foo1": "bar1","foo2": "bar2","foo3": "bar3","foo4": "bar4","foo5": "bar5","foo6": "bar6"}'       


def decode_b():
    json.loads(bdata)

def decode_u():
    json.loads(udata)

def decode_x():
    if isinstance(udata, unicode):
        x = udata.encode('utf-8')
    else:
        x = udata
    json.loads(x)


import timeit

def bench():
    print("bytes:      ", timeit.timeit(decode_b, number=100000))
    print("unicode:    ", timeit.timeit(decode_u, number=100000))
    print("pre encode: ", timeit.timeit(decode_x, number=100000))

for _ in range(10):
    bench()

result

$ ~/local/pypy-2.6.0-osx64/bin/pypy bench.py
bytes:       0.121253013611
unicode:     0.51861000061
pre encode:  0.186152935028
bytes:       0.13639998436
unicode:     0.485965013504
pre encode:  0.139013051987
bytes:       0.105733156204
unicode:     0.441829919815
pre encode:  0.130655050278
bytes:       0.110300064087
unicode:     0.454895019531
pre encode:  0.13870716095
bytes:       0.108355045319
unicode:     0.525803804398
pre encode:  0.164574146271
bytes:       0.146996974945
unicode:     0.561616182327
pre encode:  0.157838821411
bytes:       0.123056173325
unicode:     0.532580137253
pre encode:  0.152902841568
bytes:       0.122449874878
unicode:     0.563801050186
pre encode:  0.170814990997
bytes:       0.104251861572
unicode:     0.508492946625
pre encode:  0.177821874619
bytes:       0.12731218338
unicode:     0.492110967636
pre encode:  0.137986898422