[Tutor] script comparing two values - ASCII encoding error

[Jeff Shannon]

Mic Forster wrote:

>I repeated the code you recommended and had no
>problem. All of the sudden this started happening:
>

I don't see offhand anything that should be causing a UnicodeError.  Can 
you give us the complete traceback that you're getting?  Those few lines 
that precede the "UnicodeError: ..." bit can tell us a lot about where 
your problem is...

However, I'd like to point out one thing...

>>>>def f(k, s):
>>>>        
>>>>
>        return k / (1-k) * (1-k)**s / (1-(1-k)**s)
>

You should probably add some parens to this -- as it is, it could be 
read two different ways (depending on which has higher priority, 
multiplication or division -- I can't remember offhand which is higher 
priority, which says to me that relying on priority is a bad idea). 
 Those two ways are:

   ( k / (1-k) ) * ( (1-k)**s / (1-(1-k)**s) )
or
    k / ( (1-k) * (1-k)**s) / (1-(1-k)**s)

I think the first is what you meant, but since I'm not certain which way 
Python will read it, I'd recommend being explicit about it.

For that matter, your last subexpression, 1-(1-k)**s, is slightly vague 
too -- should that be (1-(1-k))**s, or 1-((1-k)**s)??  I'm pretty sure 
that Python will presume the latter, and I believe that that's what you 
want, but it never hurts to add parens to make it explicit.  I'm a big 
fan of using lots of parens in complicated mathematical expressions -- 
extra parens don't hurt, and may make the intended order more clear.  

I'm also a big fan of using intermediate variables to split complicated 
expressions into two or more lines, and I'd probably write the above 
function like this:

def f(k, s):
    subterm = (1-k)**s
    return ( k / (1-k) ) * (subterm / (1-subterm) )

This makes the function a little easier to read, and also emphasises the 
symmetry involved (and, as a side bonus, saves you time by calculating 
the exponent only once).  Of course, this is really just a matter of 
taste...

Jeff Shannon
Technician/Programmer
Credit International