from __future__ import division
numbers_list = ['1','5','6','7']
operations_list = ['+','-','*','/']
result = 21
L=len(numbers_list)
def permutations(iterable, r=None):
# permutations('ABCD', 2) --> AB AC AD BA BC BD CA CB CD DA DB DC
# permutations(range(3)) --> 012 021 102 120 201 210
pool = tuple(iterable)
n = len(pool)
r = n if r is None else r
if r > n:
return
indices = range(n)
cycles = range(n, n-r, -1)
yield tuple(pool[i] for i in indices[:r])
while n:
for i in reversed(range(r)):
cycles[i] -= 1
if cycles[i] == 0:
indices[i:] = indices[i+1:] + indices[i:i+1]
cycles[i] = n - i
else:
j = cycles[i]
indices[i], indices[-j] = indices[-j], indices[i]
yield tuple(pool[i] for i in indices[:r])
break
else:
return
def main():
for numbers in permutations(numbers_list,4):
for operations in permutations(operations_list,3):
operation = (op for op in operations)
expression = ['(']*(L-1)
for i,number in enumerate(numbers):
if i==0:
expression += number
continue
expression += operation.next()
expression += number
expression += ')'
expression = ''.join(expression)
calc = eval(expression)
print '%s = %5.1f' % (expression,calc)
if round(calc)==result:
return
main()