Flask：获取过滤器的上下文

Question

我是flask的初学者，我想练习filter，我看过官方的documentation，但是没有用。

我想创建一个firstof 过滤器，即输出第一个不为“false”的参数变量。（与Django 的firstof 相同）。

<h1>Hi, {{ "username, 'guest'"| firstof }} </h1>

@app.route('/')
def index():
    return render_template('index.html')  # expect output: Hi, guest
    # return render_template('index.html', username='Carson')  # Hi, Carson

我试试，

@app.template_filter('firstof')
def firstof_filter(s: str):
    """
    USAGE::

        {{ "var1, var2, 'default_val'" | firstof }}
    """
    for data in s.split(','):
        data = data.strip()
        if data[0] == data[-1] and data[0] in ("'", '"'):
            return data[1:-1]  # a constant
        """ # does any similar grammar like below?
        if hasattr(app.current.context, data):
            return app.current.context[data]
        """

如果您能提供更多关于烧瓶过滤器的链接，那就太好了。谢谢！

Answer 1

我自己找到了答案。

直接用 Flask 来实现并不容易。

因为

# flask.templating.py

def render_template(template_name_or_list, **context):
    ctx = _app_ctx_stack.top
    ctx.app.update_template_context(context)  # it does not store the context in the ctx. it just adds something to the context
    return _render(
        ctx.app.jinja_env.get_or_select_template(template_name_or_list),
        # ctx.app.jinja_env is an environment (It combined Flask and Jinja, pretty like the Jinja.Environment)
        # get_or_select_template, will run our function and no passing the context so that is why it so hard to do it.
        context,
        ctx.app,
    )

def _render(template, context, app):
    # It seems we can't do anything when the process already here.
    before_render_template.send(app, template=template, context=context)
    rv = template.render(context)
    template_rendered.send(app, template=template, context=context)
    return rv

但我们得到一个线索，我们可以更改Jinja.Environment。

您可以在继续之前先引用Custom Filters。

解决方案和演示

from flask import render_template
from jinja2 import contextfilter
from flask.helpers import locked_cached_property
from flask import Flask
from jinja2.runtime import Context
from flask.templating import Environment
from typing import Dict
from pathlib import Path

@contextfilter
def firstof_filter(ctx: Context, s: str):
    ctx: Dict = ctx.parent
    for data in s.split(','):
        data = data.strip()
        if data[0] == data[-1] and data[0] in ("'", '"'):
            return data[1:-1]  # a constant
        if data in ctx:
            return ctx[data]

class MyFlask(Flask):
    @locked_cached_property
    def jinja_env(self):
        env: Environment = self.create_jinja_environment()
        env.filters['firstof'] = firstof_filter  # well, this way is not smart, you are better build a register to get all the filters that you have defined.
        return env

app = MyFlask(__name__, template_folder=Path('./templates'))


@app.route('/')
def test():
    return render_template('test.html', username='Carson') + '\n' + render_template('test.html')


app.run(debug=True)

在哪里 test.html

<h1>Hi, {{ "username, 'guest'"| firstof }} </h1>

附言

env.filters['firstof'] = firstof_filter嗯，这种方式不聪明。你最好建立一个注册来获取你定义的所有过滤器。

您可以参考Django:django.template.library.py -> class Library收集所有filters...

输出

Hi, Carson
Hi, guest