"""Response to StackOverflow Question: https://stackoverflow.com/q/62377553/2694511"""
from collections import defaultdict
num = ['0', '2', '3', '0','7']
letters = ['a', 'b', 'c', 'd','e']
num_letter_dict = defaultdict(list)
for n, letter in zip(num, letters):
num_letter_dict[n].append(letter)
print(num_letter_dict)
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