How do I merge a 2D array in Python into one string with List Comprehension?

Question

List Comprehension for me seems to be like the opaque block of granite that regular expressions are for me. I need pointers.

Say, I have a 2D list:

l         


        

Answer 1

My favorite, and the shortest one, is this:

li2 = sum(li, [])

and

s = ','.join(li2)

EDIT: use sum instead of reduce, (thanks Thomas Wouters!)