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

[Chris Angelico]

On Sat, Apr 5, 2014 at 3:10 PM, Mark H Harris <harrismh777 at gmail.com> wrote:
> 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

If it's too much work to make the changes to move something from
Python 2.7 to Python 3.3, it's *definitely* too much work to rewrite
it in a different language. There would have to be some strong other
reason for shifting, especially since there's a 2to3 but not a
PytoRuby. And forking is a pretty huge job; someone's gotta maintain
it. What's more likely is that, once python.org stops maintaining
Python 2.x at all, people will just stay on 2.7.9 or whatever the last
version is, without any bugfixes. Companies like Red Hat will be
looking at security patches (which is what PEP 466 is all about), but
only to the extent that they have people willing to put in the work to
make and test them. After that, it'll be like running old versions of
anything else: you weigh the cost of migrating to the new version
against the risk of exploits if you don't move. It's that simple.

ChrisA