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