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

[Josiah Carlson]

Heiko Wundram <me+python-dev at modelnine.org> wrote:
> Why isn't this good practice? It's not always sensible to refactor loop code 
> to call methods (to make the loop body shorter), and it's a pretty general 
> case that you only want to iterate over part of a generator, not over the 
> whole content. Because of this, list comprehensions grew the 'if'-clause. So: 
> why doesn't the for-loop?

List comprehensions grew an if clause because they are expressions that
were supposed to replace one of the most the most common idioms in
Python:

    x = []
    for i in ...:
        if ...:
            x.append(...)

And you know what?  They've done that very well.  Seemingly so well that
you are asking for the list comprehension syntax to make it back into
for loops.  So far, you have failed to convince me (and most others it
looks like) that it is a good idea, you have re-hashed the same
arguments you made in the PEP, and Guido chimed in as the first message
to say:

    "-1. The contraction just makes it easier to miss the logic."
    "This was proposed and rejected before."
    - Guido

If you want some advice: let it drop.


 - Josiah