Chris Rebert wrote:
On Fri, Jun 19, 2009 at 10:54 AM, Mathias Panzenböck<grosser.meister.morti@gmx.net> wrote:
You could write: [x|y <- l, x <- [f(y)], x > 0]
Oh, wait. Thats Haskell. And even in haskell you would write: [x|x <- map f l, x > 0]
In Python you can write: [x for x in map(f,l) if x > 0]
In Python 2.x you may want to write: from itertools import imap [x for x in imap(f,l) if x > 0]
A more SQL like approach that would fit somewhat with pythons syntax would be (as you can see its exactly the same lengths as the above but needs a new name): [f(x) as y for x in l if y > 0]
Because in SQL you can write (IIRC): select f(x) as y from l where y > 0;
Maybe something like .Nets LINQ would be a nice idea to integrate in python?
Comprehensions and generator expressions already give us most of the LINQ functionality. Add in `list()` and the ability to `.sort()` lists with a `key` argument and you have the entire thing, except for the one corner case being discussed. Unless I've overlooked something...
Yes: With LINQ its possible to build a query object out of an LINQ expression instead of evaluating it eagerly. This is used primarily to generate SQL code while still using syntax native to the host language (C#) and preserving type safety (ok the later cannot be done in python). -panzi