int 不是可迭代的 python

我正在尝试创建 Cows and Bulls 游戏，但得到了一个TypeError: 'int' object is not iterable. 这是我的代码：

import random

print('You are playing Cows and Bulls game !')

number = random.randint(1000,2000)
number = list(number)
print(number)
user_number = input('Guess a number : \n')
global cows, bulls
cows = 0
bulls = 0
user_number = list(user_number)
print(user_number)

def game():
 if user_number[0] in number:
    cows += 1
 elif user_number[1] in number:
    cows += 1
 elif user_number[2] in number:
    cows += 1
 elif user_number[3] in number:
    cows += 1
 elif user_number not in number:
    bulls += 1

game()

当我启动程序时，它给了我：

Traceback (most recent call last):
    File "C:\Users\user\AppData\Local\Programs\Python\Python37-32\Cows and
        number = list(number)
TypeError: 'int' object is not iterable

我不知道该怎么办，请帮忙，我刚刚开始，所以可能会有一些愚蠢的错误，如果是这样，请务必纠正我:) 我想它想让我把它变成一个字符串还是什么？