flask 源码专题（九）：flask扩展点

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")

执行顺序

2. request_started = _signals.signal('request-started')                # 请求到来前执行
5. request_finished = _signals.signal('request-finished')              # 请求结束后执行
3. before_render_template = _signals.signal('before-render-template')  # 模板渲染前执行
4. template_rendered = _signals.signal('template-rendered')            # 模板渲染后执行
                 
发生在2/3/4/5或不执行 got_request_exception = _signals.signal('got-request-exception')    # 请求执行出现异常时执行
                 
6. request_tearing_down = _signals.signal('request-tearing-down')      # 请求执行完毕后自动执行（无论成功与否）
7. appcontext_tearing_down = _signals.signal('appcontext-tearing-down')# 请求上下文执行完毕后自动执行（无论成功与否）     
1. appcontext_pushed = _signals.signal('appcontext-pushed')            # 请求app上下文push时执行
                
8. appcontext_popped = _signals.signal('appcontext-popped')            # 请求上下文pop时执行
                
message_flashed = _signals.signal('message-flashed')                   # 调用flask在其中添加数据时，自动触发

自定义信号

　第一步：创建信号

   第二步：将函数注册到信号中： 添加到这个列表

　第三步： 发送信号

　第四步：运行

 具体实现：可参考flask源码，写一个自定义信号

from flask import Flask,flash
from flask.signals import _signals
app = Flask(__name__)

xinhao = _signals.signal("xinhao")#创建信号
#定义函数
def wahaha(*args,**kwargs):
    print("111",args,kwargs)

def sww(*args,**kwargs):
    print("222",args,kwargs)
# 将函数注册到信号中,添加到这个列表
xinhao.connect(wahaha)
xinhao.connect(sww)

@app.route("/zzz")
def zzz():
    xinhao.send(sender='xxx',a1=123,a2=456)  #触发这个信号，执行注册到这个信号列表中的所有函数,此处的参数个数需要与定义的函数中的参数一致
    return "发送信号成功"

if __name__ == '__main__':
    app.run(debug=True)
    
#打印结果
# 111 (None,) {'sender': 'xxx', 'a1': 123, 'a2': 456}
# 222 (None,) {'sender': 'xxx', 'a1': 123, 'a2': 456}