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

[Brian Quinlan]

> I'd love to "get" why some form of assignment on the fly is so evil
that
> we have to invent hacks to work around its lack over and over again
> (recipie 1.9 in the Cookbook).  The lack interacts especially badly
with 
> a language where indentation is a mandantory part of the control
> structure.  :-(

People make frequent mistakes with inline assignment in other languages
(e.g. C), so it shouldn't be allowed. I don't think that indentation has
anything to do with this.

> So the typical processing loop is conceptually simple in a language
very
> similar to Python:
> 
>   for l in file.readlines():
>     if (m = re1.match(l)):
>       (first, second, ...) = m.groups()
>       process type 1 record ...
>     elif (m = re2.match(l)):
>       ...
>     ...

I'd write that as:

def process_type_1(first, second, ...):
    process type 1 record ...

def process_type_2(first, second, ...):
    process type 2 record ...

processing_rules = [(r'....', process_type_1),
			  (r'....', process_type_2),
                    ...]


compiled_rules = [(exp.compile(), func) for (exp, func) in
processing_rules]

for l in file.readlines():
    for exp, func in compiled_rules:
        match = exp.match(l)
        if match is not None:
             apply(func, m.groups())
             break

Notice that:
- it is very easy to add new record types
- record processing is more modular
- the code is pretty simple
 
Cheers,
Brian