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")

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