[Edu-sig] re: Python as a first-year programming language

[Terry Hancock]

On Monday 28 April 2003 09:29 am, Kirby Urner wrote:
> On Monday 28 April 2003 01:37 am, Toby Donaldson wrote:
> Is there any way in Python to implement 
non-deterministic
> > programming, e.g. for backtacking? It would be nice to 
be able to write
> > something like this:
> >
> >   def triple(a, b, c, n):
> >     a = choice(n)    # choice non-deterministically 
chooses a number from 0
> > to n-1
> >     b = choice(n)
> >     c = choice(n)
> >     if a**2 + b**2 == c**2:
> >       return a, b, c
> 
> You're asking if Python can do pseudo-random numbers?  

Assuming that you *did* mean this, Toby, you should be aware
that your function can be written almost exactly as you 
just did:

from random import choice

def triple(n):
    a = choice(range(n)) 
    b = choice(range(n))
    c = choice(range(n))
    if a**2 + b**2 == c**2:
        return a, b, c

Try it.  ;-)
>>> triple(3)
>>> triple(3)
(2, 0, 2)
>>> triple(3)
(1, 0, 1)
>>> triple(3)
>>> triple(3)
(0, 0, 0)

I have to admit that I don't understand why you want this 
(I'm sure there's a good reason, and I'm hoping you'll tell 
me so I'll know too ;-) ).   Is this for some kind of 
search efficiency reason?  I have a feeling you're using 
theory I never got because I never formally studied 
programming.

Kirby's point of course (due to being a philosopher? ;-) ) 
is that such numbers aren't *truly* random.  Which of course
they aren't.  But they're "pretty random" -- without knowing
the application, I couldn't say if they were "random 
enough".  I have seen Monte Carlo simulation applications 
which required *incredibly* well-distributed random numbers 
with no cycles less than several billion (we were doing 
forward-ray-tracing of billions of simulated photons to 
build up enough to create an image -- you have to do this 
in the forward direction rather than the usual reverse ray
tracing in some scientific applications).  I was actually 
surprised to find out that random number algorithms that 
good exist!

Cheers,
Terry

--
Terry Hancock ( hancock at anansispaceworks.com )
Anansi Spaceworks  http://www.anansispaceworks.com