def METHOD_NAME(self, param_type, special_arguments={}):
    """A helper function to build a widget type from a template.
    It passes to the created widget generator a series of common
     parameters, plus the ones needed to specialize the given template
    @param param_type: the template to specialize
    @param special_arguments: the arguments used for this particular widget
                              generator.
    @return function: return a widget generator, not a widget. the widget
                       can be obtained by calling widget_generator(backend)
    """
    return lambda backend: param_type(req=self.req,
                                      backend=backend,
                                      width=self.COMMON_WIDTH,
                                      **special_arguments)