如何在循环内存储函数返回语句的值而不会出现类型错误？

Question

我正在尝试制作一个程序，我需要调用每次检查差异的函数，并将其存储在一个变量中。问题是我得到一个 TypeError。这个问题的解决方案是什么？

尝试将函数分配给一个变量，这样每次调用时它都会更新。

代码如下：

def difference(word):
    counter = 0
    difference = 0
    for letter in word_one:   
        if letter != word[counter]:
            difference += 1
        counter += 1
    return difference


global difference
global word
attempts = 0
word = ''

global word_one
global word_two
word_picker()


print("Turn this word: "+str(word_one))
print("Into this word: "+str(word_two))
print()


while word != word_two:
    word = input("Enter word: ")
    word = list(word)
    word_one = list(word_one)
    word_two = list(word_two)
    difference = difference(word)
    if difference > 1:
        print("You can only change one letter at a time!")
        print()