Explanation of this Python language feature? [x for x in x for x in x] (to flatten a nested list)

[Roy Smith]

In article <533fd894$0$29993$c3e8da3$5496439d at news.astraweb.com>,
 Steven D'Aprano <steve+comp.lang.python at pearwood.info> wrote:

> Twisted has apparently said they cannot migrate to 3.x. They might, I 
> suppose, take up maintenance of Python 2.7. But I doubt it. I expect 
> that when push comes to shove in 4 or 5 years time, they'll find a 
> way to migrate.

Is Twisted really that relevant?  I know they've been around for a long 
time, and there are a few high-profile projects using them, but I get 
the impression they've become a bit of a legacy product by now, and 5 
years from now, I suspect that will be even more true.

Their big claim to fame was the ability to do asynchronous I/O in 
Python.  There's other ways to do that now.

> Nobody is *afraid* of a fork. But forks do split the community, and 
> introduce FUD 

A classic example would be the BSD world (Free, Net, Open, Dragonfly, 
and a host of minor players).  There's a lot of really smart people 
working on those projects, but they're all pushing in different 
directions.  Meanwhile, Linux ate their lunch.

>> Somebody should
>> put a date on C python 3.4+ migration and cut off support for 2.7.x/
> 
> 2045-04-01. If you're not migrated to Python 3.4 by then, no cake for you.

But, somewhere, somebody will still be running XP on their desktop, and 
haggling with Microsoft over another deadline extension.