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

[88888 Dihedral]

> >>> x = [[1, 2], [3, 4]]
> 
> >>> for x in x:
> 
> ...     for x in x:
> 
> ...         print(x)
> 
This is valid in the syntax level 
in python. But it is only good
for those  writing obscure programs in 
my opinions at most team works.