[Discuss] Interpreters vs Compilers

[Alan W. Irwin]

On 2008-03-12 10:26-0700 John Blomfield wrote:

> My presentation "Writing programs for Linux" at last night's monthly meeting 
> gave rise to some spirited discussion, when I remarked that compiled 
> languages resulted in faster execution times than interpreted languages and 
> tended to be preferred by programmers for larger more complex problems. 
> There were many reasons put forward as to why this should be and some doubted 
> there was any significant difference in practice.  I was unable to answer 
> these questions authoritatively since I just use a language when it suits my 
> particular purpose and use the rule of thumb "big or fast program = C or C++" 
> and "small and quick to write = Python, bash etc."
>
> The attached link is a result of a quick google that tends to support my 
> pragmatic view of life:
> http://furryland.org/~mikec/bench/

The "speed" benchmark there (which was simply an empty loop with many
iterations) confirmed what I said at the meeting; loops are really
inefficient for both perl and python.  You get roughly a factor of 200
decrease in speed in the python case and roughly a factor of 100 in the perl
case compared to C++.  There was a thread sometime ago here on relative
speeds of python/perl/C where David Bronaugh did some tests which also told
a similar story for a loop which did a simple calculation (addition of
integers?) within the loop.

The question I really would like to see answered is why are both perl and
python so slow on loops? I hypothesized last night that the interpreter did
some compilation for each iteration of the loop, but it was asserted that
interpreters only do the compilation of the code in loops once.  I don't
believe for an instant that some difference in optimization (another
possible explanation discussed last night for the slowness of python and
perl for loops) is going to cause a two orders of magnitude change in speed.
So does anybody have the authorative answer to this question?

I enjoyed your talk, John.  There was something for everybody there, but
unfortunately those who as yet have not programmed at all were (AFAICT)
underrepresented in the audience.  I recommend you make the presentation
available on our website so those who missed the talk can benefit.

Alan
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Alan W. Irwin

Astronomical research affiliation with Department of Physics and Astronomy,
University of Victoria (astrowww.phys.uvic.ca).

Programming affiliations with the FreeEOS equation-of-state implementation
for stellar interiors (freeeos.sf.net); PLplot scientific plotting software
package (plplot.org); the libLASi project (unifont.org/lasi); the Loads of
Linux Links project (loll.sf.net); and the Linux Brochure Project
(lbproject.sf.net).
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Linux-powered Science
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