Iterate through two lists of different lengths

Question

I have the following two lists:

nums = [1, 2, 3, 4, 5, 6, 7, 8]

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

for x, y in nums, ltrs:
    print(x, y)

With the following error

c:\Python35\Scripts>python listtest.py
Traceback (most recent call last):
  File "listtest.py", line 5, in <module>
    for x, y in nums, ltrs:
ValueError: too many values to unpack (expected 2)

I would like for the output to be:

1a, 2b, 3c, 4d, 5, 6, 7, 8

From what I have read the zip method will only work if the two lists are the same length, what are my options with lists of different lengths?

Answer 1

izip_longest is similar to zip, but allows you to add a default value (fillvalue) to use when the shorter list is exhausted. From there on, it's just some simple manipulations:

[''.join([str(c) for c in x]) for x in izip_longest(nums, ltrs, fillvalue='')]

Answer 2

You can use itertools.zip_longest for Python3:

import itertools
nums = [1, 2, 3, 4, 5, 6, 7, 8]
ltrs = ['a', 'b', 'c', 'd']
final_list = [''.join([str(c) if isinstance(c, int) else c for c in [i for i in b if i is not None]]) for b in itertools.zip_longest(nums, ltrs)]

Output:

['1a', '2b', '3c', '4d', '5', '6', '7', '8'] 

Answer 3

import itertools
for x, y in list(itertools.zip_longest(nums,ltrs)):
  print(x, y)

Output

1 a
2 b
3 c
4 d
5 None
6 None
7 None
8 None