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

[Mark H Harris]

On 4/4/14 6:16 PM, Mark Lawrence wrote:
> Fear/panic of a fork, where did that come from?  It's certainly the
> first I've ever heard of it.
>

hi Mark, it came from Ian; or, my interpretation of Ian. It comes out on 
the net too (from various places). Here is Ian's quote, then my comment:

> Eventually users still on 2.x will need to upgrade, but you
> can't force them to do it on your own schedule.  That path will just
> end up driving them to another language, or to a fork of 2.7.

The sentiment behind this last quote is essentially fear (and that is 
natural). Its basically the tension between (I'm speaking as the royal 
we here) we don't want folks to be driven away from Cpython as a 
language, and we don't want them to fork the Cpython interpreter, so 
we'll take a very casual and methodically conservative approach to 
nudging people towards a Cpython3 migration route ( I am speaking not 
for the community, just hypothetically trying to get at the gist of 
Ian's quote);  please forgive me if I didn't quite get it.

I spent most of the afternoon reading this:

> http://python-notes.curiousefficiency.org/en/latest/python3/questions_and_answers.html

This doc is long, thorough in detail, and mostly complete. Its a great 
read. The migration is not trivial, and it can't happen in one fell 
swoop, either.


marcus