Writing more efficient code

Diez B. Roggisch deets at nospam.web.de
Mon Jan 1 23:04:23 CET 2007


gonzlobo schrieb:
> Greetings, and happyNewYear to all.
> 
> I picked up Python a few weeks ago, and have been able to parse large
> files and process data pretty easily, but I believe my code isn't too
> efficient. I'm hoping dictionaries will help out, but I'm not sure the
> best way to implement them.
> 
> I've been using a bunch of nested if/elif/else statements to select
> slices (0317 & 03de) from a file, then parse the data (aa, hh, bb,
> d2-d9) into parameters (a = airspeed, h = heading) & flags.
> 
> #sample file contents
> 0000007d 03 0317 aa aa aa aa aa hh hh hh bb bb
> 0000007e 06 03de d2 d3 d4 d5 d6 d7 d8 d9 10 11
> 
> # some pseudo code
> if PID == '03de':
>    flapsCmd = int(d3, 16)
>   if flapsCmd == 0xc0:
>      <flaps up code>
>   elif flapsCmd == 0x03:
>      <flaps down code>
> if PID == '0317':
>   airspeed == 'combine aa for airspeed & multiply by 0.1'
>   heading == 'combine hh for heading'
>   mach == 'combine bb for mach & multiply by 0.01'
> 
> Might dictionaries help in this case... say Label0317(parameterName,
> slice (d3), scaleFactor(0.1))... I'd like to use them if they'll
> replace the dozens of nested conditionals.  I have roughly 75
> different parameters to decode from a file containing ~2.5 million
> lines of data.
> 
> I know my pseudo code lacks details, but hopefully I'm getting my
> point across...
> 
> (I suppose switch/select/case statements would help a bit, but python
> doesn't seem to use them... not to start a religious war or anything).

The dictionary approach certainly will be speedier - lookup should 
usually be O(1) instead of O(n) for the if-elif-chain.

Diez



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