[Python-Dev] efficient string concatenation (yep, from 2004)

[Lennart Regebro]

> Something is needed - a patch for PyPy or for the documentation I guess.

Not arguing that it wouldn't be good, but I disagree that it is needed.

This is only an issue when you, as in your proof, have a loop that
does concatenation. This is usually when looping over a list of
strings that should be concatenated together. Doing so in a loop with
concatenation may be the natural way for people new to Python, but the
"natural" way to do it in Python is with a ''.join() call.

This:

    s = ''.join(('X' for x in xrange(x)))

Is more than twice as fast in Python 2.7 than your example. It is in
fact also slower in PyPy 1.9 than Python 2.7, but only with a factor
of two:

Python 2.7:
time for 10000000 concats = 0.887
Pypy 1.9:
time for 10000000 concats = 1.600

(And of course s = 'X'* x takes only a bout a hundredth of the time,
but that's cheating. ;-)

//Lennart