docs: def update_asset(self, asset_form=None):
          """Updates an existing asset.
  
          :param asset_form: the form containing the elements to be updated
          :type asset_form: ``osid.repository.AssetForm``
          :raise: ``IllegalState`` -- ``asset_form`` already used in anupdate transaction
          :raise: ``InvalidArgument`` -- the form contains an invalid value
          :raise: ``NullArgument`` -- ``asset_form`` is ``null``
          :raise: ``OperationFailed`` -- unable to complete request
          :raise: ``PermissionDenied`` -- authorization failure
          :raise: ``Unsupported`` -- ``asset_form`` did not originate from ``get_asset_form_for_update()``
  
          *compliance: mandatory -- This method must be implemented.*
  
          """
          if asset_form is None:
              raise NullArgument()
          if not isinstance(asset_form, abc_repository_objects.AssetForm):
              raise InvalidArgument('argument type is not an AssetForm')
          if not asset_form.is_for_update():
              raise InvalidArgument('form is for create only, not update')
          try:
              if self._forms[asset_form.get_id().get_identifier()] == UPDATED:
                  raise IllegalState('form already used in an update transaction')
          except KeyError:
              raise Unsupported('form did not originate from this session')
          if not asset_form.is_valid():
              raise InvalidArgument('one or more of the form elements is invalid')
  
          url_path = construct_url('assets',
                                   bank_id=self._catalog_idstr)
          try:
              result = self._put_request(url_path, asset_form._my_map)
          except Exception:
              raise  # OperationFailed()
          self._forms[asset_form.get_id().get_identifier()] = UPDATED
          return objects.Asset(result)