Speed of string += string

[Alan McIntyre]

Alan McIntyre wrote:
> Now I'm inclined to do a comparison just for my own curiosity's 
> sake...maybe I'll be back with graphs in just a bit. :)

Here's the times required for adding 200k two-character strings to a 
single string (in steps of 1000 += operations):

http://norfolkgraphics.com/testing/test.png

The green line is for Python, red for C++.  It looks kind of O(n)'ish 
for both of them.

Each point in the graph corresponds to the time required to perform 1000 
+= operations (the Python version of the code is below).  I dumped the 
output of the Python and C++ programs to text files and used SciPy to 
plot them.

The total run time for the Python version was 194.069 seconds, the C++ 
std::string version was 157.386 seconds.   I would have done a plain C 
version but my curiosity ran out and it's too nice outside. ;)

Full disclosure: The C++ program was compiled with Borland C++ Builder 
5, all optimizations turned on; the Python program is just as you see it 
below, run on Python 2.2.2 (binary install release from python.org). 
YMMV.  IANAL.

----------------------------------------------------------
import time

x = []
t = []
s = ''

starttime = time.time()

for i in range(200):
     ts = time.time()
     for j in range(1000):
         s += 'aa'

     x.append(i)
     t.append(time.time()-ts)

runTime = time.time() - starttime

for i in range(len(x)):
     print '%d, %.3f' % (x[i], t[i])

print '\nTotal run time: %.3f' % runTime