get sum by two string

sumByString.py

"""
@desc get sum by two string
@param string s1
@param string s2
@return string
"""
def sumByString(s1, s2):
    s1 = s1.rjust(len(s2), '0')
    s2 = s2.rjust(len(s1), '0')
    
    a = list(s1[::-1])
    b = list(s2[::-1])
    s = ''
    f = '0'
    for i in range(len(a)):
        c = int(a[i]) + int(b[i]) + int(f)
        s += str(c % 10)
        f = int(c / 10)
    if int(f) > 0:
        s += str(f)
    return s[::-1]


# r = sumByString('1234243243245','42342342456')
# print(r)
# 1276585585701