Python 2.7 Performance Comparison: list concatenation (+) vs list.extend()

gistfile1.py

mek@bigbertha:~/7-Projects$ python
Python 2.7.2+ (default, Oct  4 2011, 20:06:09) 
[GCC 4.6.1] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import time
>>> def test():
...     """Comapring concat. + vs list.extend"""
...     x = range(10000000)
...     y = range(10000000)
...     x0 = time.clock()
...     z = x + y
...     t1 = time.clock() - x0
...     x1 = time.clock()
...     x.extend(y)
...     t2 = time.clock() - x1
...     print "+ takes %s, extend takes %s" % (t1, t2)
... 
>>> test()
+ takes 0.31, extend takes 0.12

I can confirm these results: https://pastebin.com/rYbfXQDp

My averages after running this program five times are the following:

Concat average: 2.711305618286133e-07
Extend average: 2.4134492874145505e-07

Concat average: 2.803680896759033e-07
Extend average: 2.349388599395752e-07

Concat average: 3.220231533050537e-07
Extend average: 2.413630485534668e-07

Concat average: 2.821462154388428e-07
Extend average: 2.3563313484191895e-07

Concat average: 2.739343643188477e-07
Extend average: 2.407205104827881e-07

In all cases, extend beat concat

But extend is in-place and adding like this is not (compared to +=)... right?

@colllin This is so long enough ago that I don't remember the context of this. But yeah. I'm fairly sure .extend(...) is an in-place operation and += is not (creates a new list).