When Python outruns C++ ...

Jacek Generowicz Jacek.Generowicz at cern.ch
Mon Mar 31 21:53:09 CEST 2003


Alex Martelli <aleax at aleax.it> writes:

> I'm putting the final touches on a talk I'll give to PythonUK next
> week (it's held together with the ACCU conference) on "Python for
> C++ and Java programmers".  One example I give is a task for which
> C++ is quite suited, with its standard library -- reading a text file,
> breaking it into whitespace-separated 'words', building an index from
> each word to the line numbers on which it appears, and showing the
> index with words in alphabetical order, one per line, each followed
> by the line numbers on which it appears.
> 
> Thanks to the excellent support given for these tasks by the standard
> library, the C++ source is ONLY twice as big as the Python source for
> the same job (a more usual ratio is around 5:1).  This holds for both
> the simplest versions, and the slightly more complicated ones with
> somewhat better optimization.  The runtimes on my box (Linux Mandrake
> 9.0, gcc 3.1, Python 2.3) are, when the programs are run on the 4.4 MB
> of the "King James Bible" in plain ASCII text: 17.4 seconds for the
> simplest C++, going down to 15 with optimizations; 11.2 seconds for the
> simplest Python, going down to 8.1 with optimizations (CPU times are
> in very similar ratios).

Will you make this code public ?

Having a few examples of this sort readily available could be very
useful when trying to make the point that the belief that C++ is
absolutely essential for writing fast code, is slightly, errm,
misguided.

> By writing Python first, you'll often get an application with
> acceptable performance; if not, you profile it, find out the
> hot-spots, optimize those in Python terms, and if that's still not
> enough, it's EASY to recode the hot-spots in faster ways while still
> leaving MOST of your application in Python.

And it's even more difficult to convince people of this truth (just as
it would be more difficult to write a demonstration of it, but it
wouldn't surprise me if you had one of those too :-)




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