relative speed of incremention syntaxes (or "i=i+1" VS "i+=1")

[Laurent]

Hi Folks,

I was arguing with a guy who was sure that incrementing a variable i with "i += 1" is faster than "i = i + 1". I couldn't tell if he was right or wrong so I did a little benchmark with the very useful timeit module.
Here are the results on my little Linux Eeepc Netbook (using Python 3.2):


Computing, please wait...

Results for 1000000 times "i = i + 1":
0.37591004371643066
0.3827171325683594
0.37238597869873047
0.37305116653442383
0.3725881576538086
0.37294602394104004
0.3712761402130127
0.37357497215270996
0.371567964553833
0.37359118461608887
Total 3.7396 seconds.

Results for 1000000 times "i += 1":
0.3821070194244385
0.3802030086517334
0.3828878402709961
0.3823058605194092
0.3801591396331787
0.38340115547180176
0.3795340061187744
0.38153910636901855
0.3835160732269287
0.381864070892334
Total 3.8175 seconds.

==> "i = i + 1" is 2.08% faster than "i += 1".



I did many tests and "i = i + 1" always seems to be around 2% faster than "i += 1". This is no surprise as the += notation seems to be a syntaxic sugar layer that has to be converted to i = i + 1 anyway. Am I wrong in my interpretation?

Btw here's the trivial Python 3.2 script I made for this benchmark:


import timeit

r = 10
n = 1000000

s1 = "i = i + 1"
s2 = "i += 1"

t1 = timeit.Timer(stmt=s1, setup="i = 0")
t2 = timeit.Timer(stmt=s2, setup="i = 0")

print("Computing, please wait...")

results1 = t1.repeat(repeat=r, number=n)
results2 = t2.repeat(repeat=r, number=n)

print('\nResults for {} times "{}":'.format(n, s1))
sum1 = 0
for result in results1:
	print(result)
	sum1 += result
print("Total {:.5} seconds.".format(sum1))

print('\nResults for {} times "{}":'.format(n, s2))
sum2 = 0
for result in results2:
	print(result)
	sum2 += result
print("Total {:.5} seconds.".format(sum2))

print('\n==> "{}" is {:.3}% faster than "{}".'.format(s1,(sum2 / sum1) * 100 - 100, s2))



Comments are welcome...