ValueError：以10为基数的int（）的无效文字如何修复错误

import random
import operator


op = {"+":operator.add,
      "-":operator.sub,
      "*":operator.mul}
num1 = random.randint(0,10)
num2 = random.randint(0,10)
ops = random.choice(list(op.keys()))
print (num1 + int(ops) + num2)

我正在尝试进行随机数学问题测验，但无法弄清楚为什么我会不断收到错误：

Traceback (most recent call last):
  File "N:/Computer science/A453/Test.py", line 12, in <module>
    print (num1 + int(ops) + num2)
ValueError: invalid literal for int() with base 10: '-'
>>> ================================