Вот такую тестовую программу написал:
namesList = []
authorsList = []
with open('Saves/names file.txt', 'r') as namesFile:
for line in namesFile:
appendData = line.lower()
namesList.append(appendData)
with open('Saves/authors file.txt', 'r') as authorsFile:
for line in authorsFile:
appendData = line.lower()
authorsList.append(appendData)
for x in range(0, len(namesList)):
print(namesList[x], authorsList[x])
И вывод программы:
book 1
author 1
book 2 author 2
book 2 author 2 выводится правильно, а book 1 author 1 нет