08 Flask源码剖析之flask拓展点

1. 信号（源码）

信号，是在flask框架中为我们预留的钩子，让我们可以进行一些自定义操作。
```
pip3 install blinker
```

2. 根据flask项目的请求流程来进行设置扩展点

中间件

# 代码示例

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。

# 代码示例

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__

执行before_first_request扩展

# 代码示例

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

# 代码示例

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

# 代码示例

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

# 代码示例

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()

视图函数

before_render_template / rendered_template

# 代码示例

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

# 代码示例

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

# 代码示例

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

# 代码示例

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

# 代码示例

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

# 代码示例

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_popped

# 代码示例

from flask import Flask,render_template,g

from flask import signals

app = Flask(__name__)

@signals.appcontext_popped.connect

def f14(app):

    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()

扩展:flash

flash存值之后只能取一次

# 代码示例

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()

总结：

关于flask内部共有14+个扩展点用于我们对flask框架内部进行定制，其中有：9个是信号。

# 源码示例

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")