list comprehensions whats happening here

[Terry Reedy]

> For example,
>
>  >>> [[i,j] for i in (0,) for j in ('a', 'b', 'c')]
> [[0, 'a'], [0, 'b'], [0, 'c']]
>
> prepends 0 to all members of the list;
> I also believe that the idiom above will turn out
> to be the fastest way to prepend all elements of a list with something,
> without using any extra space, or calling any user defined function.

Uh, no.
[[0,j] for j in ('a','b','c')] is much cleaner and faster.  Methinks
turning a constant into a pseudovariable is the wrong way to go.

Terry J. Reedy