extract elements of n char from a list

[Fernando Perez]

Alex Martelli wrote:

> It's the best Python technique of all to learn to MEASURE rather
> than having to ASK.  Set up a little benchmark script and use it.
> THEN you can ask here if the results aren't convincing to you (it's
> quite possible to get things wrong).  Tim Peters' introduction
> to the Algorithms chapter of "Python Cookbook" (the printed edition
> that O'Reilly just launched) is invaluable in showing you exactly
> how to perform such little benchmarks for accuracy and solidity.

I Haven't had the chance to read the Cookbook yet, so I'm sure my solutions 
may have holes in them. But coincidentally this morning I just finished 
writing a benchmarking package for my own use, and since this kind of 
question seems to come up often, I figured I'd post it for other's benefit. 
Go to http://windom.colorado.edu/~fperez/python/ and click on the 
benchmarking link.

It's a Linux/Unix package, as it implements clocks to accurately distinguish 
between system and user time consumed by your process. Some examples taken 
from the docs:

In [1]: from benchmark import timer

In [2]: def loop(n):
   ...:     for i in range(n):
   ...:         pass
   ...:

In [3]: timer(loop,100000)
Out[3]: 0.10000000000000009

In [4]: timer.report(loop,100000)
Timing report
-------------
Function tested     : <function loop at 0x82afc04>
Number of calls     : 1
Total execution time: 0.1 s

In [5]: timer.status()
Object: <benchmark.timing.GenericTimer instance at 0x82f43cc>
Object's __dict__ :
mode        : user
ncalls      : 1
print_args  : 0
print_output: 0
stream      : <open file '<stdout>', mode 'w' at 0x8100a50>

In [6]: timer.ncalls = 5

In [7]: timer.mode = 'all'

In [8]: timer.report(loop,100000)
Timing report
-------------
Function tested     : <function loop at 0x82afc04>
Number of calls     : 5
Total execution time:
              system: 0.01 s
              user  : 0.52 s
Average time per call:
               system: 0.002 s
               user  : 0.1 s


Well, I hope it's useful for some.

Cheers,

f.