processing of list of list

Question

I am working on lists of list

input:

x = [['a','a','a'],['b','b','b'],['c','c','c'],['d','d','d']]

and am looking for an output:

s = ['a_b_c_d','a_b_c_d','a_b_c_d']

Kindly let me know how can I do this using list comprehension.

Answer 1

>>> x = [['a','a','a'],['b','b','b'],['c','c','c'],['d','d','d']]
>>> map('_'.join, zip(*x))
['a_b_c_d', 'a_b_c_d', 'a_b_c_d']

… although @aix's list comprehension is more list-comprehensible.