reverse-integer

Given a 32-bit signed integer, reverse digits of an integer.

Example 1:

Input: 123
Output: 321
Example 2:

Input: -123
Output: -321
Example 3:

Input: 120
Output: 21
Note:
Assume we are dealing with an environment which could only store integers within the 32-bit signed integer range: [−231,  231 − 1]. For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.
My code:
import numpy as np
class Solution:
    def reverse(self, x):
        """
        :type x: int
        :rtype: int
        """
        if x>2**31-1 or x<-2**31:
            return 0
        flag=False
        if x<0:
            x=abs(x)
            flag=True
        tmp_list=[]
        remain=0
        while x!=0:
            remain=x%10
            #print('remains now %d'%remain)
            tmp_list.append(remain)
            x=int(np.floor(x/10))
            #print(x)
        new_x=0
        for i in range(len(tmp_list)):
            index=i
            #print(tmp_list[index])
            new_x=new_x*10+tmp_list[index]
        if new_x>2**31-1 or new_x<-2**31:
            return 0
        if flag:
            return -new_x
        return new_x
            
Solution:
https://leetcode.com/problems/reverse-integer/description/