Dynamic Dictionary Creation

[David Eppstein]

In article <3DF0EE53.62F70405 at kootenay.com>,
 Bob van der Poel <bvdpoel at kootenay.com> wrote:

> def getNoteLen(x):
>    global TicksQ
>    ntb = { '1': TicksQ *
> 4,                                                               
>       '2': TicksQ * 2,                                   
>       '4': TicksQ,
>       '8': TicksQ
> }                                                                  
>                                                                               
>                                                   
>    return ntb[str(x)]  
> 
> What I'm concerned about is the initialization of the table. Am I
> correct in assuming that each time I access the function the values in
> the table will be recalculated?
> 
> I suppose I could make the table global and avoid this?
> 
> I could avoid runtime math by replacing TicksQ with a value, but I've
> always been taught not to use literal magic numbers, and python doesn't
> have a DEFINE statement.

What's wrong with

def getNoteLen(x): return TicksQ * 4.0 / x

?

If what you are really trying to do is some arithmetic, but you're doing 
it by converting the input number to a string and doing a table lookup 
to emulate the arithmetic operations, then trying to optimize the table 
lookup seems like the wrong place to look for more efficiency.

-- 
David Eppstein       UC Irvine Dept. of Information & Computer Science
eppstein at ics.uci.edu http://www.ics.uci.edu/~eppstein/