Add Two Very Big Numbers (say 100 digits)

def sumBig(s,t):
    """s and t are two numbers represented as lists"

    n = len(s) - 1
    m = len(t) - 1
    carry = 0
    o = [] #output

    while True:
        o.append((s[n] + t[m] + carry) % 10)
        carry = (s[n] + t[m] + carry) / 10
        n -= 1
        m -= 1
        if n == -1 or m == -1:
            break
    
    while m > -1:
        o.append((t[m] + carry) % 10)
        carry = (t[m] + carry) / 10
        m- = 1
        
    while n > -1:
        o.append((t[n] + carry) % 10)
        carry = (t[n] + carry) / 10
        n -= 1

    if carry == 1: #checks to see if at the end of adding digits there is a carry over left
	o.append(1) 

    o.reverse()    
    return o
        
print sumBig([4,2,3],[9,9,6,6,8])