Number trick (always gets 13)

number_trick.py

def get_max_exponent (n):
    n_copy = int(n)
    n_max = 0
    while True:
        div = 10**n_max
        if (n_copy//div)*div == 0:
            break
        n_max += 1
    return n_max - 1 #To get the break condition, it's needed the first exponent larger than the number

def get_digits (n):
    sum = []
    n_copy = int(n)
    n_max = get_max_exponent (n_copy)
    for exp in xrange(n_max,0,-1):
        div = 10**exp
        parcel = n_copy//div
        sum.append(parcel)
        n_copy -= div*parcel
    sum.append(n_copy)
    return sum

def sum_list (list):
    sum = 0
    for member in list:
        sum += member
    return sum
    
def f (n):
    sum = 9*n
    i = 0
    while sum > 10:
        digits = get_digits(sum)
        sum = sum_list(digits)
    sum += 4
    return sum
    
if __name__ == '__main__':
    for i in xrange(1,110):
        print i, i*9, get_digits(i*9), f(i)