[Tutor] Cython question

[Alan Gauld]

"Albert-Jan Roskam" <fomcl at yahoo.com> wrote 

> I used cProfile to find the bottlenecks, the two 
> Python functions getValueChar and getValueNum. 
> These two Python functions simply call two equivalent 
> C functions in a .dll (using ctypes). 

In that case cythin will speed up the calling loops 
but it can't do anything to speed up the DLL calls, 
you have effectively already optimised those 
functions by calling the DLL.

> The problem is that these functions are called 
> as many times as there are VALUES in a file 

It might be worth a try if you have very big data sets
because a C loop is faster than a Python loop. 
But don't expect order of magnitude improvements.

> So if I understand you correctly, this is not Cpu 
> bound and, therefore, alas, Cython won't improve 
> the excution time. Correct?

It may still be CPU bound in that the CPU is doing 
all the work, but if the CPU time is in the DLL 
functions rather than in the loop cython won't 
help much.

CPU bound refers to the type of processing - is 
it lots of logic, math, control flows etc? Or is 
it I/O bound - reading network, disk, or user input?
Or it might be memory bound - creating lots of 
in memory objects (especially if that results in 
paging to disk, when it becomes I/O bound too!)

Knowing what is causing the bottleneck will 
determine how to improve things. Use tools like
TaskManager in Windows or top in *nix to see 
where the time is going and what resources are 
being consumed. Fast code is not always the 
answer.

HTH,

-- 
Alan Gauld
Author of the Learn to Program web site
http://www.alan-g.me.uk/