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

[Roy Smith]

In article <j8-dne29t9g2VarOnZ2dnUVZ_qSdnZ2d at giganews.com>,
 Larry Hudson <orgnut at yahoo.com> wrote:

> I believe the point is your generalized use of "American".  After all, 
> Mexicans are Americans too, as well as Canadians, Peruvians and ...
> 
> Unfortunately, there is no good word for "USA-ian".

I believe Mexicans refer to us as "norteamericanos" in polite company.  
That's a little long for daily use, so more typically it's shortened to 
"gringo".