求各位大佬解答一下我的问题：我的代码出现了什么问题

with open("prime_numbers_file.txt", "a+") as file:
    prime_numbers = file.read()   
    a = b = 0
    c = prime_numbers.split()
    d = len(c) ** 2 - 1
    e = c[-1]
    f = 1