[Python] timeit versus timing decorator

I'm trying to time some code. First I used a timing decorator:

#!/usr/bin/env python

import time
from itertools import izip
from random import shuffle

def timing_val(func):
def wrapper(*arg, **kw):
'''source: http://www.daniweb.com/code/snippet368.html'''
t1 = time.time()
res = func(*arg, **kw)
t2 = time.time()
return (t2 - t1), res, func.__name__
return wrapper

@timing_val
def time_izip(alist, n):
i = iter(alist)
return [x for x in izip(* * n)]

@timing_val
def time_indexing(alist, n):
return [alist[i:i + n] for i in range(0, len(alist), n)]

func_list = [locals()[key] for key in locals().keys()
if callable(locals()[key]) and key.startswith('time')]
shuffle(func_list) # Shuffle, just in case the order matters

alist = range(1000000)
times = []
for f in func_list:
times.append(f(alist, 31))

times.sort(key=lambda x: x[0])
for (time, result, func_name) in times:
print '%s took %0.3fms.' % (func_name, time * 1000.)


yields

% test.py
time_indexing took 73.230ms.
time_izip took 122.057ms.


And here I use timeit:

% python - m timeit - s '' 'alist=range(1000000);[alist[i:i+31] for i in range(0, len(alist), 31)]'
10 loops, best of 3:
64 msec per loop
% python - m timeit - s 'from itertools import izip' 'alist=range(1000000);i=iter(alist);[x for x in izip(**31)]'
10 loops, best of 3:
66.5 msec per loop


Using timeit the results are virtually the same, but using the timing decorator it appears time_indexing is faster than time_izip.

What accounts for this difference?

Should either method be believed?

If so, which?

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