Python Decimal To Binary

toBinary.py

import math
def toBinary(num):
    powers = []
    while num > 0:
        power = int(math.log(num)/math.log(2))
        powers.append(power)
        num -= pow(2, power)
    i = 0
    binaryString = ""
    while len(powers) > 0:
        if (i in powers):
            binaryString = "1" + binaryString
            powers.remove(i)
        else:
            binaryString = "0" + binaryString
        i += 1
    return binaryString