Python and STL efficiency

[Maric Michaud]

Tim, sorry for I send it to you personally, I was abused by thunderbird.

Tim N. van der Leeuw a écrit :

> 
> Your C++ version got me the following timings (using gcc 3.4.5 as the
> compiler, MinGW version, with -O6):
> 
> ...
> 
> 
> Hmmm... Can we conclude now that carefully crafted C++ code is about
> twice as fast as casually and intuitively written Python code? ;) (Just
> kidding here of course)

Every C++ code must be carefully crafted :).

But your benchmark surprise me, here is what I get on my windows box :

Python2.4 :
===========

maric at aristote-2 /cygdrive/c/Documents and Settings/maric/Bureau
$ which python2.4
/usr/bin/python2.4

maric at aristote-2 /cygdrive/c/Documents and Settings/maric/Bureau
$ which python
/cygdrive/c/Python24/python

maric at aristote-2 /cygdrive/c/Documents and Settings/maric/Bureau
$ python2.4 testpython.py
so long...
What do you know
fool
chicken crosses road
Elapsed: 3.655000 seconds

maric at aristote-2 /cygdrive/c/Documents and Settings/maric/Bureau
$ python testpython.py
so long...
What do you know
fool
chicken crosses road
Elapsed: 3.077764 seconds

Cygwin version is slower, but not too much.

C++, compiled with VS2005, release, no other configuration :
============================================================

print_occurence_of_strings
What do you know?
chicken crosses road
fool
so long...
print_occurence_of_unique_strings
What do you know?
chicken crosses road
fool
so long...
print_occurence_of_unique_strings_compared_by_address
What do you know?
chicken crosses road
fool
so long...
strings : 16.718 # memory allocation is quite bad
unique strings : 1.188
compared by address : 0.453

C++, with gcc 3.3/Cygwin
========================

maric at aristote-2 /cygdrive/c/Documents and Settings/maric/Bureau
$ g++ -O3 -o testcpp testcpp.cpp

maric at aristote-2 /cygdrive/c/Documents and Settings/maric/Bureau
$ ./testcpp
print_occurence_of_strings
What do you know?
chicken crosses road
fool
so long...
print_occurence_of_unique_strings
What do you know?
chicken crosses road
fool
so long...
print_occurence_of_unique_strings_compared_by_address
What do you know?
chicken crosses road
fool
so long...
strings : 17.266 # still bad
unique strings : 1.547
compared by address : 0.375

Hum, with my old gcc I get equal or better performances than with VS2005.

Finally, the equivalent code is still about 10x faster in c++ than in 
Python, as it was on my Linux box.



Mc Osten a écrit :
...
 > However, I would have written the code using a proper compare function
 > rather than using two sets. In this particular case the number of
 > elements of the first set is negligible in respect of the initial vector
 > size, thus copying it again does not take a lot of time.
 > But such code is optimized for the problem itself: in the real world I

Of course, it's a quick hack to get the same behavior.

 > suppose we would have passed set a proper comparison function that
 > checks address and then string equality.
 >

Yes, furthermore, that is *exactly* what the python code is doing (see 
my other post to Fredrik).


-- 
_____________

Maric Michaud
_____________

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