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")