comefrom: <qiyuangong>136_Single_Number_2.py
code: def singleNumber( nums):
      s = set()
      for num in nums:
          if num in s:
              s.remove(num)
          else:
              s.add(num)
      return s.pop()
masked: def sample_funcname ( var_0 ) :
      var_2 = set ( )
      for var_3 in var_0 :
          if var_3 in var_2 :
              var_2.remove ( var_3 )
          else :
              var_2.add ( var_3 )
      return var_2.pop ( )
  