hailstone.py

import sys

hailrecord = {1:0, 2:1}

def is_int(s):
    try:
        int(s)
        return True
    except ValueError:
        return False

def hailstone(n, prt, opt):
    if n < 1:
        print "Pick a positive number, dummy."
        return -1
    elif not is_int(n):
        print "That's not a number, dummy."
        return -1
    else:
        n = int(n)
        steps = 0
        while n <> 1:
            if opt:
                if n in hailrecord:
                    return hailrecord[n] + steps
            if prt: print n,
            steps += 1
            if n % 2 == 0:
                n = n / 2
            else:
                n = n * 3 + 1
        if prt: print n
        return steps

if __name__ == '__main__':
    if (len(sys.argv) < 2 or len(sys.argv) > 3):
        print "You done goofed!"
        sys.exit(1)
    else:
        if sys.argv[1] == "find":
            goal = int(sys.argv[2])
            if not is_int(goal):
                print "That goal's not a number, dummy."
                sys.exit(1)
            else:
                num = 2
                s = 0
                while s < goal:
                    num += 1
                    if num in hailrecord:
                        temp = hailrecord[num]
                    else:
                        temp = hailstone(num, False, True)
                    if temp > 0 and temp > s:
                        s = temp
                    elif temp < 0:
                        sys.exit(2)
                hailstone(num, True, False)
                print num, "has a hailstone sequence of length", s
        else:
            num = sys.argv[1]
            hailstone(num, True, False)