Why is Python popular, while Lisp and Scheme aren't?

[Alex Martelli]

Martin Maney wrote:
   ...
> Think about the straightforward implementation of this in legal Python
> with less undersized indentation than I used before:

[KNode doesn't display your tabs in this reply, so I don't know if they 
remained or not -- you can use spaces if you want to avoid such issues).


> for l in lines:
> m = re1.match(l)
> if m:
> ... process type 1
> else:
> m = re2.match(l)
> if m:
> ... process type 2
> else:
> m = re3.match(l)
> if m:
> ... process type 3

Flat is better than nested:

for l in lines:
    m = re1.match(1)
    if m:
        ...process type 1...
        continue
    m = re2.match(1)
    if m:
        ...process type 2...
        continue
    m = re3.match(1)
    if m:
        ...process type 3...
        continue

or probably better, putting the "processtype" into functions:

for l in lines:
    for are, processtype in zip((re1,re2,re3),(pt1, pt2, ptr)):
        m = are.match(l)
        if m:
            processtype(m)
            break
    else:
        nomatchfor(l)

exhibiting even better the commonality of structure (IMHO).


I've found myself wishing for "set-and-test" basically in ONE
kind of situation: when I was transcribing algorithms coded in
languages that used that form, such as C.  In such cases, of
course, it's trivially easy to build and use set-and-test, see:

http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/66061


Alex