leetcode Single Number python

#question : Given an array of integers, every element appears twice except for one. Find that single one.
#note : Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?

class Solution(object):
    def singleNumber(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        intlen=len(nums)
        if intlen == 0:
            return -1
        if intlen == 1:
            return nums[0]

        ans=nums[0]
        for i in range(1,intlen):
            ans = ans ^ nums[i]

        return ans