Iterating through list of list without knowing number of inner lists

Question

I have a list of list:

x = [[1,2,3], [4,2], [5,4,1]]

I want to traverse the elements in the inner list sequentially and get:

1 4 5
2 2 4
3 None 1

I've tried this but I couldn't get the last line:

>>> x = [[1,2,3], [4,2], [5,4,1]]
>>> a, b, c = x
>>> for i,j,k in zip(a,b,c):
...     print i,j,k
... 
1 4 5
2 2 4

Given that I don't know how many inner lists are there how do i do achieve the desired result?

Answer 1

You can use itertools.izip_longest to pad the shorter sublists:

for t in izip_longest(*x):
    print t

Note the use of *x and t to deal with an unknown number of sublists.

Answer 2

from itertools import izip_longest
x = [[1,2,3], [4,2], [5,4,1]]
for i in izip_longest(*x):
    print i

(1, 4, 5)
(2, 2, 4)
(3, None, 1)