Brute Force 8s Puzzle

eights.py

#!/usr/bin/env python3
import random

choices = list('8+*-/')
result = None
while result != 100:
    eights_left = 8
    expr = ''
    on_operator = True
    while eights_left > 0:
        if on_operator:
            # on operator, next element needs to be an eight
            expr = expr + '8'
            eights_left -= 1
            on_operator = False
        else:
            # on an eight, next element can be anything
            elem = choices[random.randint(0, len(choices) - 1)]
            expr = expr + elem

            if elem == '8':
                eights_left -= 1
            else:
                on_operator = True
    try:
        result = eval(expr)
    except Exception as e:
        print('Invalid expression?')
        print(expr)

print(expr)