code: def single_number(nums):
      """
      Returns single number, if found.
      Else if all numbers appear twice, returns 0.
      :type nums: List[int]
      :rtype: int
      """
      i = 0
      for num in nums:
          i ^= num
      return i
  
label_desc: Use image node_id 1 for calling a global function with example usage: single_number(nums) and returns: i