powofthree.py

def is_power_of_three(num):
    from types import IntType, FloatType
    assert type(num) in (IntType, FloatType)
    x = 3
    if num in (0, 1): return True
    elif num < 0: return False
    elif num > 0 and num < 1:
        while True:
            y = 1.0/x  #hacky..
            #print y, x
            if y == num: return True
            elif y < num: return False
            else: x = x*3
    else:
        while True:
            if x == num: return True
            elif x > num: return False
            else: x = x*3

def test_is_power_of_three():
    for i in (0,1,2,3,9,10,27,81,59049,123456789012,
          -1,0.5,float(1.0/3),float(1.0/9),
          'abc',012,True):
        print i
        try: print is_power_of_three(i)
        except: print 'Type error'