proper loop syntax?

sismex01 at hebmex.com sismex01 at hebmex.com
Mon Aug 11 18:20:39 CEST 2003


heh heh :-)

Congratulations on picking python, you'll have lotsa hours
of pure python programming penjoyment (ok, so I dont have
impeccable spelling) ;-)

Anyway.  What we have here, is the need of more data-oriented
coding, and not necessarily a lot of chained if-elif-elif...
statements.

> mask = "XXNNxxASSs" 
> 
> for t in range(licenses):   # licenses = 5 
> 
>  for y in mask: 
>      if y == "x": 
>          if t == 0: 
>            license_char = "5" 
>          elif t == 1: 
>            license_char = "P" 
....
>      elif y == "a" or "S": 
>         if t == 0: 
>            license_char = "T" 
>         elif t == 1: 
>            license_char = " " 
....
>      elif y == "X" or "s": 
>         if t == 0: 
>            license_char = "7" 
>         elif t == 1: 
>            license_char = "G" 
....
>      license = license + license_char 

So, you´re only testing a few variables: "y" and "t",
and they have pre-known values in each case, and also,
it´s a simple translation.

You can create a dictionary-of-lists which will
do all of the decision's regarding the selection of
license_char without the if´s.  Something like:

MAIN = {}
MAIN["x"] = [ "5", "P", ... ]
MAIN["a"] = [ "T", " ", ... ]
MAIN["S"] = MAIN["a"]
MAIN["X"] = [ "7", "G", ... ]
MAIN["s"] = MAIN["X"]

So, in this "pseudo-matrix", all decisions are already
taken, there´s no need to be iffing around with fixed
values and translations; this is data-oriented programming.

Now your loop becomes:

for t in range(licenses):
    license = ""
    for y in mask:
        license = license + MAIN[y][t]
    print license


As to why if-elif-elif... doesn´t perform as we think it
does, I´ve never had to investigate it.  So much decisions
sometimes means that the algorith must be rethought into
a better one.

HTH!

-gustavo
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