code: def add_tag(self, key, value=''):
          
          status = self.connection.create_tags([self.id], {key : value})
          if self.tags is None:
              self.tags = TagSet()
          self.tags[key] = value
docs: Add a tag to this object.  Tag's are stored by AWS and can be used
          to organize and filter resources.  Adding a tag involves a round-trip
          to the EC2 service.
  
          :type key: str
          :param key: The key or name of the tag being stored.
  
          :type value: str
          :param value: An optional value that can be stored with the tag.
                        If you want only the tag name and no value, the
                        value should be the empty string.