[Python-Dev] PEP-xxx: Unification of for statement and list-comp syntax

[Heiko Wundram]

Am Sonntag 21 Mai 2006 22:11 schrieb Talin:
> As a general guideline, I've noticed that proposals which are purely
> syntactic sugar are unlikely to be accepted unless there is some
> additional benefit other than just compression of source code.

I know about this, but generally, I find there's more to this "syntactic 
sugar" than just source code compression.

1) It unifies the syntax for list comprehensions and for loops, which use the 
same keywords (and are thus identified easily). Basically, you can then think 
of a for-loop as a list comprehension which evaluates a suite instead of an 
expression, and doesn't store the evaluated items, or vice versa, which at 
the moment you can't, because of the difference in setup.

2) Just as I've replied to Terry J. Reed, if you find list comprehensions easy 
to read, you're also bound to be able to understand what "for <expr> in 
<expr> if <expr>:" does, at least AFAICT.

3) Generally, indentation, as Terry J. Reed suggested, isn't always good. If 
the body of the loop is more than a few lines long (which happens more often 
than not in my code), extra indentation is bound to confuse me. That's why I 
use "if not <expr>: continue" at the moment, so that I don't need extra 
indentation. If I could just append the condition to the loop to get it out 
of the way (just as you do with a list comprehension), I save the 
obnoxious "if not <expr>: continue" (which destroys my read flow of the body 
somewhat too), and still get the same behaviour without any extra 
(errorprone, in my eyes) indentation.

Anyway, it's fine if Guido says this is -1. I don't need to discuss this, as I 
guess it's a pretty futile attempt to get people to consider this against 
Guido's will. I just found this to be something I'd personally longed for for 
a long time, and had time free today, so I thought I'd just implement it. ;-) 

And, additionally, nobody's keeping me from making my own Python tree where I 
can keep this patch for my very personal scripts where I don't need to have 
interoperability. This is open source, isn't it? ;-)

--- Heiko.