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

[Mark H Harris]

On 4/3/14 12:14 PM, Marko Rauhamaa wrote:
> Mark H Harris <harrismh777 at gmail.com>:
>
>> So, python(3)'s use of unicode is exciting, not only as a step forward
>> for the python interpreter, but also as a leadership step forward in
>> computer science around the world.
>
> Big words. I don't think computer science has experienced major steps
> forward since the 1930's: combinatory logic, the Turing machine, the
> Entscheidungsproblem, the halting problem,...
>
> The one major latter-day addition is complexity theory (1960's).

hi Marko,  computer science covers everything from a linked list to 
virtual reality, from cpu pipe lining to flash memory, from punched tape 
i/o to plasma displays--- to led back-lit flat panels. Computer science 
also includes theory, and most of what you mention actually had its 
beginnings in mathematics, not computer science. And yet, most of what 
you mention as fundamental to computer science is only the beginning.

The Turning a-machines together (and parallel to) Alonzo Church's lambda 
calculus (diverse methodologies on computability) brought a negative 
answer on the Entscheidungsproblem; so much so that one might even think 
that artificial intelligence were impossible. Alan Turning proved 
(before computers ever existed) that one a-machine may not determine 
whether another a-machine configuration will loop or halt. So what? Do 
we cease to work towards artificial intelligence? Do you believe that 
the AI work at MIT (using lisp) was a non step forwards for artificial 
intelligence; for computer science?

Did not David Hilbert get a kick-in-the-pants? You might have thought 
that mathematics at IAS would have folded its tents and blown away after 
Kurt Gődel proved (mostly as consequence of self-reference) that if an 
axiomatic system is complete it is also inconsistent, and if consistent 
assuredly incomplete!  There are true statements which cannot be proven! 
  Oh, crap. There must be systems of computation for which there is no 
proof, yet function non-the-less. Does this impact computer science 
today; does this impact AI studies today?

We as human beings have only just begun. The human mind is a quantum 
computer. Can a bit be 1 and 0 at the same time??  It most certainly 
can; entanglement is a computational reality that we have only just 
begun to think about let alone comprehend, nor code for (whatever we 
might mean by that).

Mathematicians hate this, but, computers are the way forward for 
mathematics. Computer proofs are increasing; we are discovering that 
proofs of import are requiring computers and computation algorithms. We 
don't through our straight edges and compasses away; nor do we toss out 
our BIC pens and paper. Algorithm is what is needed because the 
mathematics is too complicated. Computer science is moving understanding 
forward with algorithm.

Beyond all of that is communication. That is where unicode comes in. 
Computer science is going to handle the problem of Universal 
Translation. Great strides have been taken towards this already. More 
are sure to come.

שלם

marcus