code: def in6_6to4ExtractAddr(addr):
      
      try:
          addr = inet_pton(socket.AF_INET6, addr)
      except:
          return None
      if addr[:2] != b" \x02":
          return None
      return inet_ntop(socket.AF_INET, addr[2:6])
docs: Extract IPv4 address embbeded in 6to4 address. Passed address must be
      a 6to4 addrees. None is returned on error.