Leetcode(7)——Reverse Integer

import math
class Solution(object):
def reverse(self, x):
"""
:type x: int
:rtype: int
"""
x1 = abs(x)
if x==0:
flag=0
else:
flag=x1/x
str=[]
while x1!=0:
ys=x1%10
str.append(ys)
x1=(x1-ys)/10
L=len(str)
x1=0
ind=0
while ind<len(str):
x1=x1+str[ind]*(10**(len(str)-ind-1))
ind=ind+1
if x1<2**31:
return x1*flag
else:
return 0