flask中有大量的信号的使用，在信号执行时我们就可以对它进行一个功能定制，而要想做到定制功能，那么就得明白它在flask生命周期中的哪个部分。下面来简单看看它有哪些地方可以定制功能。

信号分类：

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")

下面是根据流程，可能 的扩展点：

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__

执行before_first_request扩展

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

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

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

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()

before_render_template / rendered_template

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

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

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

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

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

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

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()

在flask文档中，连接数据库时就用到了其中的teardown_request,和before_request, 分别用来断开，建立 数据库连接。

import sqlite3
from flask import g

DATABASE = '/path/to/database.db'

def connect_db():
    return sqlite3.connect(DATABASE)

@app.before_request
def before_request():
    g.db = connect_db()

@app.teardown_request
def teardown_request(exception):
    if hasattr(g, 'db'):
        g.db.close()

 

其中的g是在flask请求周期内可以全局调用的变量。