code: def get_attribute(self, attrkey, as_string=False, as_list=False):
          
          assert not as_string or not as_list
          if attrkey not in self._attrs:
              return None
          if attrkey == 'ID':
              return self._attrs[attrkey]
          attrvalues = list(self._attrs[attrkey])
          attrvalues.sort()
          if len(attrvalues) == 1 and not as_list:
              return attrvalues[0]
          elif as_string:
              return ','.join(attrvalues)
          return attrvalues
docs: Get the value of an attribute.
  
          By default, returns a string for ID and attributes with a single value,
          and a list of strings for attributes with multiple values. The
          `as_string` and `as_list` options can be used to force the function to
          return values as a string (comma-separated in case of multiple values)
          or a list.