code: def append(self, cpe):
          
  
          if cpe.VERSION != CPE.VERSION_1_1:
              msg = "CPE Name version {0} not valid, version 1.1 expected".format(
                  cpe.VERSION)
              raise ValueError(msg)
  
          for k in self.K:
              if cpe.cpe_str == k.cpe_str:
                  return None
  
          self.K.append(cpe)
docs: Adds a CPE Name to the set if not already.
  
          :param CPE cpe: CPE Name to store in set
          :returns: None
          :exception: ValueError - invalid version of CPE Name
  
          TEST:
  
          >>> from .cpeset1_1 import CPESet1_1
          >>> from .cpe1_1 import CPE1_1
          >>> uri1 = 'cpe://microsoft:windows:xp!vista'
          >>> c1 = CPE1_1(uri1)
          >>> s = CPESet1_1()
          >>> s.append(c1)