container.py 文件源码

def render(self, ctx=None):
        '''
        Only render if condition applies

        :param ctx: rendering context in which the method was called
        :rtype: `Bits`
        :return: rendered value of the container
        '''
        if ctx is None:
            ctx = RenderContext()
        self._initialize()
        if self in ctx:
            self._current_rendered = self._in_render_value()
        else:
            ctx.push(self)
            if self._evaluate_condition(ctx):
                super(Conditional, self).render(ctx)
            else:
                self.set_current_value(empty_bits)
            ctx.pop()
        return self._current_rendered