大数加法 big number add

n = 55
def add(a, b):
while len(a) < n:
a = "0" + a
while len(b) < n:
b = "0" + b

sum = []
for _ in range(0, n):
sum.append(0)

i = n-1
while i > 0:
s = int(a[i]) + int(b[i]) + sum[i]
if s < 10:
sum[i] = s
else:
sum[i] = s - 10
sum[i-1] = 1 + sum[i-1]
i -= 1

result = ''
for i in range(0, n):
result += str(sum[i])

return result

#a = "37107287533902102798797998220837590246510135740250"
#b = "46376937677490009712648124896970078050417018260538"
#print add(a,b)

final = ""
for _ in range(0, n):
final += "0"

f1 = file('input.txt')
while 1:
line = f1.readline()
if len(line) == 0:
break
line = line.strip("\r\n")
final = add(line , final)

print len(final)
print final
print final.strip("0")
print final.strip("0")[0:10]

f1.close()