Decomposer

#!/usr/bin/env python

# This program decomposes the number 'exp' into a sum of powers of 2

import sys

fail = 'Must give me a positive integer fella'

try:
    exp = int(sys.argv[1])
except:
    sys.exit(fail)

if (exp <= 0):
    sys.exit(fail)

i = 0 # exponent
num = 0 # number to compare with exp
last = 0 # an helper variable
factors = list() # list of factors

while (exp > 0):
    while (num < exp):
        last = num
        num = 2**i
        i = i+1
    if (num == exp):
        exp = exp-num
        factors.append(num)
    else:
        exp = exp-last
        factors.append(last)
    i = 0
    num = 0

print factors