Endorsement of list comprehensions

[Colin J. Williams]

Michael Chermside wrote:

> Carsten Gehling writes:
> > Okay I understand everyting except this contruct:
> >
> > keys = [d[0] for d in cursor.description]
> >
> > Let me guess: it loops through cursor.description (obvious), for each of the
> > items (which are tuples) it "outputs" element 0. The output is then
> > automatically formatted in a way, that conforms to the list creation syntax.
> >
> > Or something like that. Kind of neat - haven't seen that in any other
> > language, that I've used.
>
> YES! Exactly!
>
> This is a feature called "list comprehensions", and it works just like
> you describe. You type out:
>
>     [ func_using_var for var in some_list if condition_using_var ]
>
> and Python makes that into the following loop:
>
>     aList = []
>     for var in some_list:
>         if condition_using_var:
>             aList.append( func_using_var )
>     return aList
>
> (except, of course, that there's no "aList" variable... python just
> uses the list that would be generated that way).
>
> The original idea comes from "Haskell", another cool programming
> language, and the strongest argument I've EVER heard for why this
> is a good feature is the little "stream-of-consciousness" description
> you just gave which seems to show that as a new-to-python programmer,
> it took you only a few moments to figure it out (correctly!) on your
> own!
>
> Thanks for endorsing one of my favorite Python features!
>
> -- Michael Chermside

You wrote:
   [ func_using_var for var in some_list if condition_using_var ]

It might be slightly more generally be expressed as:
   [expr_using_var for var in some_list if condition_using_var ]

Colin W.