帮助自定义Jinja2扩展 [英] Help with custom Jinja2 Extension

问题描述

我一直在努力使这个Jinja2自定义扩展能够正常工作-当他们说写一个不适合平民"的文档时，他们并没有开玩笑-最终设法找到了这个工作代码:

I've struggled to get this Jinja2 custom extension to work -- the docs weren't kidding when they said writing one was not for "civilians" -- and finally managed to arrive at this working code:

class WrapperExtension(Extension):

    tags = set(['wrap'])

    def parse(self, parser):
        lineno = parser.stream.next().lineno
        args = [parser.parse_expression()]
        args.append(nodes.Const(args[0].name))
        return nodes.CallBlock(
            self.call_method('_render', args),
            [], [], []).set_lineno(lineno)

    def _render(self, value, name, *args, **kwargs):
        if some_condition():
            return '<wrapper id="%s">%s</wrapper>' % (name, value)
        return value

正如我所说，这现在正在起作用.我不确定的是为什么我需要在parse()中返回nodes.CallBlock，而不是self.call_method()(它返回一个nodes.Call对象).如果有人有任何见识-或可以为我提供有关编写扩展程序的教程-请让我知道.

As I said, this is now working. What I'm unsure about is why I need to return nodes.CallBlock in parse(), rather than self.call_method() (which returns a nodes.Call object). If anyone has any insight -- or can point me to a tutorial on writing extensions -- please do let me know.

推荐答案

原因是希望parse()返回语句节点，例如CallBlock或Assign. call_method()返回一个表达式节点，必须将其包装在CallBlock中才能有一条语句.

The reason is that parse() is expected to return a statement node, such as CallBlock or Assign. call_method() returns an expression node, which you must wrap in CallBlock to have a statement.

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