Flask -- 信号等可扩展点的使用

信号

信号，是在flask框架中为我们预留的钩子，让我们可以在flask请求过程中定制一些用户行为。
依赖blinker模块：

pip3 install blinker

以下是根据flask项目的请求流程来进行可扩展点的

中间件，请求到来前

from flask import Flask,render_template

app = Flask(__name__)


@app.route('/index')
def index():
    return render_template('index.html')


@app.route('/order')
def order():
    return render_template('order.html')


class MyMiddleware(object):
    def __init__(self,old_app):
        self.wsgi_app = old_app.wsgi_app

    def __call__(self, *args, **kwargs):
        print('123')
        result = self.wsgi_app(*args, **kwargs)
        print('456')
        return result

app.wsgi_app = MyMiddleware(app)

if __name__ == '__main__':
    app.run()

当app_ctx被push到local中栈之后，会触发appcontext_pushed信号，之前注册在这个信号中的方法，就会被执行。

from flask import Flask,render_template
from flask import signals

app = Flask(__name__)

@signals.appcontext_pushed.connect
def f1(arg):
    print('appcontext_pushed信号f1被触发',arg)

@signals.appcontext_pushed.connect
def f2(arg):
    print('appcontext_pushed信号f2被触发',arg)

@app.route('/index')
def index():
    return render_template('index.html')

@app.route('/order')
def order():
    return render_template('order.html')

if __name__ == '__main__':
    app.run()
    # app.__call__

before_first_request扩展，视图函数前

from flask import Flask,render_template

app = Flask(__name__)

@app.before_first_request
def f2():
    print('before_first_requestf2被触发')

@app.route('/index')
def index():
    return render_template('index.html')

@app.route('/order')
def order():
    return render_template('order.html')

if __name__ == '__main__':
    app.run()

request_started信号，请求到来前触发执行

from flask import Flask,render_template
from flask import signals
app = Flask(__name__)

@signals.request_started.connect
def f3(arg):
    print('request_started信号被触发',arg)

@app.route('/index')
def index():
    return render_template('index.html')

@app.route('/order')
def order():
    return render_template('order.html')

if __name__ == '__main__':
    app.run()

url_value_processor 在befor_request前

from flask import Flask,render_template,g
from flask import signals
app = Flask(__name__)


@app.url_value_preprocessor
def f5(endpoint,args):
    print('f5')

@app.route('/index/')
def index():
    print('index')
    return render_template('index.html')

@app.route('/order')
def order():
    print('order')
    return render_template('order.html')

if __name__ == '__main__':
    app.run()

before_reuqest，视图函数前

from flask import Flask,render_template,g
from flask import signals
app = Flask(__name__)

@app.before_request
def f6():
    g.xx = 123
    print('f6')

@app.route('/index/')
def index():
    print('index')
    return render_template('index.html')

@app.route('/order')
def order():
    print('order')
    return render_template('order.html')

if __name__ == '__main__':
    app.run()

分割线，上面是视图函数前能触发==============

before_render_template / rendered_template ，模板渲染前后触发执行

from flask import Flask,render_template,g
from flask import signals
app = Flask(__name__)

@signals.before_render_template.connect
def f7(app, template, context):
    print('f7')

@signals.template_rendered.connect
def f8(app, template, context):
    print('f8')

@app.route('/index/')
def index():
    return render_template('index.html')

@app.route('/order')
def order():
    print('order')
    return render_template('order.html')

if __name__ == '__main__':
    app.run()

after_request，视图函数后执行

from flask import Flask,render_template,g
from flask import signals
app = Flask(__name__)

@app.after_request
def f9(response):
    print('f9')
    return response

@app.route('/index/')
def index():
    return render_template('index.html')

@app.route('/order')
def order():
    print('order')
    return render_template('order.html')

if __name__ == '__main__':
    app.run()

request_finished，请求结束后触发执行

from flask import Flask,render_template,g
from flask import signals
app = Flask(__name__)

@signals.request_finished.connect
def f10(app,response):
    print('f10')

@app.route('/index/')
def index():
    return render_template('index.html')

@app.route('/order')
def order():
    print('order')
    return render_template('order.html')

if __name__ == '__main__':
    app.run()

got_request_exception，在befor_first_request出现异常时触发，出错后不会执行视图函数，但会执行after_request.

from flask import Flask,render_template,g
from flask import signals
app = Flask(__name__)

@app.before_first_request
def test():
    int('asdf')

@signals.got_request_exception.connect
def f11(app,exception):
    print('f11')

@app.route('/index/')
def index():
    return render_template('index.html')

@app.route('/order')
def order():
    print('order')
    return render_template('order.html')

if __name__ == '__main__':
    app.run()

teardown_request,在after后

from flask import Flask,render_template,g
from flask import signals
app = Flask(__name__)

@app.teardown_request
def f12(exc):
    print('f12')

@app.route('/index/')
def index():
    return render_template('index.html')

@app.route('/order')
def order():
    print('order')
    return render_template('order.html')

if __name__ == '__main__':
    app.run()

request_tearing_down，请求执行完毕后自动执行（无论成功与否）

from flask import Flask,render_template,g
from flask import signals
app = Flask(__name__)

@signals.request_tearing_down.connect
def f13(app,exc):
    print('f13')

@app.route('/index/')
def index():
    return render_template('index.html')

@app.route('/order')
def order():
    print('order')
    return render_template('order.html')

if __name__ == '__main__':
    app.run()

appcontext_tearing_down，在Appcontext中pop 应用上下文执行完毕后自动执行（无论成功与否）

from flask import Flask,render_template,g
from flask import signals
app = Flask(__name__)

@signals.appcontext_tearing_down.connect
def f14(app, exc):
    print('f14')

@app.route('/index/')
def index():
    return render_template('index.html')

@app.route('/order')
def order():
    print('order')
    return render_template('order.html')

if __name__ == '__main__':
    app.run()

appcontext_popped,应用上下文pop时执行

from flask import Flask,render_template,g
from flask import signals
app = Flask(__name__)

@signals.appcontext_popped.connect
def f15(app):
    print('f15')

@app.route('/index/')
def index():
    return render_template('index.html')

@app.route('/order')
def order():
    print('order')
    return render_template('order.html')

if __name__ == '__main__':
    app.run()

总结：关于flask内部共有15+个扩展点用于我们对flask框架内部进行定制，其中常用的有：9个是信号。

template_rendered = _signals.signal("template-rendered")
before_render_template = _signals.signal("before-render-template")
request_started = _signals.signal("request-started")
request_finished = _signals.signal("request-finished")
request_tearing_down = _signals.signal("request-tearing-down")
got_request_exception = _signals.signal("got-request-exception")
appcontext_tearing_down = _signals.signal("appcontext-tearing-down")
appcontext_pushed = _signals.signal("appcontext-pushed")
appcontext_popped = _signals.signal("appcontext-popped")

message_flashed = _signals.signal("message-flashed")

扩展:flash 信号

flash存值之后只能取一次，调用flask在其中添加数据时，自动触发。

from flask import Flask,render_template,flash,get_flashed_messages,session
from flask import signals
app = Flask(__name__)
app.secret_key = 'iuknsoiuwknlskjdf'

@app.route('/index/')
def index():
    # flash('123')
    session['k1'] = 123
    return render_template('index.html')

@app.route('/order')
def order():
    # messages = get_flashed_messages()
    # print(messages)
    val = session['k1']
    del session['k1']
    print(val)
    return render_template('order.html')

if __name__ == '__main__':
    app.run()

posted @ 2019-11-26 18:03 SensorError 阅读(88) 评论(0) 编辑收藏举报

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