checkkmb.py

epsilon = 1e-6

def check_kmb(s: str):
    result = eval(s)
    if (686+epsilon) > result and result > (686-epsilon):
        print(s, '=', result)

def func(s: str, n: int):
    if n == 10:
        check_kmb(s)
        return
    for op in ['', '+', '-', '*', '/']:
        func(s + op + str(n), n + 1)
    
func('1', 2)

log

123-4-56+7*89 = 686
12*3+4-56+78*9 = 686
1+23+45-6+7*89 = 686
1+23*4-5*6+7*89 = 686
1+2-3+4-5+678+9 = 686
1+2*345+67-8*9 = 686
1+2*34*5+6*7*8+9 = 686
1-23-4+56/7*89 = 686.0
1-2+34+5*6+7*89 = 686
1*23-45+6+78*9 = 686
1*2+3*4-5*6+78*9 = 686
1*2-3-4-5-6+78*9 = 686
1*2*345+6+7-8-9 = 686