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

[Ian Kelly]

On Fri, Apr 4, 2014 at 2:58 PM, Mark H Harris <harrismh777 at gmail.com> wrote:
> On 4/4/14 3:20 AM, Mark Lawrence wrote:
>>
>> On 04/04/2014 03:29, Mark H Harris wrote:
>>>
>>>
>>>     Now, about Python2.  It has not died.  It appears to be 'useful'.
>>> {snip}
>>>
>>
>> For a lot of people, if it ain't broke, don't fix it.
>>
>
> hi Mark, yes that's my point. I have heard rumors of python2.8?

The Python 2.8 release schedule is documented in PEP 404:

http://legacy.python.org/dev/peps/pep-0404/

> At some
> point I would expect that the Cpython interpreter would 'freeze' and no one
> would fix it any longer. I have a serious question, namely, why does the
> Cpython community continue to suppport two interpreters rather than asking
> the Cpython user-base to migrate to Cpython3?

2.6 and 2.7 exist to ease the pain of migration, which is far from
trivial.  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.

> Oh, I have another serious question about implementations. I'm not sure
> about (50) implementations, but I know that Jython and IronPython are
> serious contenders (although, I have not, nor probably will, use them).
>
> Are the other implementation communities *also* supporting two versions of
> the language?   Is there a Jython2 &also a Jython3 ?

There is no Jython3 or IronPython3 yet.  PyPy is currently supporting
both 2.7 and 3.2.