Solution to the last question of https://blog.svpino.com/2015/05/07/five-programming-problems-every-software-engineer-should-be-able-to-solve-in-less-than-1-hour

solution.py

import itertools
import re
a = ['1','2','3','4','5','6','7','8','9']
b = ['+','-','']
p = [list(itertools.product(t,b)) for t in a]

p[-1].remove(('9','-')) #Can't have any + or - after
p[-1].remove(('9','+')) 
#[[('1', '+'), ('1', '-'), ('1', '')], 
# [('2', '+'), ('2', '-'), ('2', '')], 
# [('3', '+'), ('3', '-'), ('3', '')], 
# [('4', '+'), ('4', '-'), ('4', '')], 
# [('5', '+'), ('5', '-'), ('5', '')], 
# [('6', '+'), ('6', '-'), ('6', '')], 
# [('7', '+'), ('7', '-'), ('7', '')], 
# [('8', '+'), ('8', '-'), ('8', '')], 
# [('9', '')]]
[z.replace(' ','') for z in ([re.sub(r"(\()*(\))*(\')*(\,)*",'',str(i)) for i in list(itertools.product(*p))]) if eval(z.replace(' ','')) == 100]