flask二十: singal

一.信号介绍

Flask框架中的信号基于blinker，其主要就是让开发者可是在flask请求过程中定制一些用户行为。

简单来说就是flask在列表里面，预留了几个空列表，在里面存东西。

信号通过发送通知来帮助你解耦应用。

简言之，信号允许某个发送者通知接收者有事情发生了；

二.内置信号

安装: 

pip3 install blinker

 

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

 

三.源码

request-started、request-finished源码

class Flask(_PackageBoundObject):

    def full_dispatch_request(self):
       
        self.try_trigger_before_first_request_functions()
        try:
            # ############### 触发request_started 信号 ###############
            request_started.send(self)       
            rv = self.preprocess_request()
            if rv is None:
                rv = self.dispatch_request()
        except Exception as e:
            rv = self.handle_user_exception(e)
        response = self.make_response(rv)
        response = self.process_response(response)

        # ############### request_finished 信号 ###############
        request_finished.send(self, response=response)
        return response

    def wsgi_app(self, environ, start_response):
        
        ctx = self.request_context(environ)
        ctx.push()
        error = None
        try:
            try:
                response = self.full_dispatch_request()
            except Exception as e:
                error = e
                response = self.make_response(self.handle_exception(e))
            return response(environ, start_response)
        finally:
            if self.should_ignore_error(error):
                error = None
            ctx.auto_pop(error)

request_started

 

 

before_render_template、template_rendered源码

def render_template(template_name_or_list, **context):
    """Renders a template from the template folder with the given
    context.

    :param template_name_or_list: the name of the template to be
                                  rendered, or an iterable with template names
                                  the first one existing will be rendered
    :param context: the variables that should be available in the
                    context of the template.
    """
    ctx = _app_ctx_stack.top
    ctx.app.update_template_context(context)
    return _render(ctx.app.jinja_env.get_or_select_template(template_name_or_list),
                   context, ctx.app)

def _render(template, context, app):
    """Renders the template and fires the signal"""

    # ############### before_render_template 信号 ###############
    before_render_template.send(app, template=template, context=context)
    rv = template.render(context)
    
    # ############### template_rendered 信号 ###############
    template_rendered.send(app, template=template, context=context)
    return rv

before_render_template

 

 

got_request_exception源码

class Flask(_PackageBoundObject):

    def handle_exception(self, e):
       
        exc_type, exc_value, tb = sys.exc_info()

        # ############### got_request_exception 信号 ###############
        got_request_exception.send(self, exception=e)
        handler = self._find_error_handler(InternalServerError())

        if self.propagate_exceptions:
            # if we want to repropagate the exception, we can attempt to
            # raise it with the whole traceback in case we can do that
            # (the function was actually called from the except part)
            # otherwise, we just raise the error again
            if exc_value is e:
                reraise(exc_type, exc_value, tb)
            else:
                raise e

        self.log_exception((exc_type, exc_value, tb))
        if handler is None:
            return InternalServerError()
        return handler(e)

    def wsgi_app(self, environ, start_response):
        
        ctx = self.request_context(environ)
        ctx.push()
        error = None
        try:
            try:
                response = self.full_dispatch_request()
            except Exception as e:
                error = e
                # 这里这里这里这里这里这里这里这里这里这里这里这里 #
                response = self.make_response(self.handle_exception(e))
            return response(environ, start_response)
        finally:
            if self.should_ignore_error(error):
                error = None
            ctx.auto_pop(error)

got_request_exception

request_tearing_down、appcontext_pushed、appcontext_popped源码

def flash(message, category='message'):
    """Flashes a message to the next request.  In order to remove the
    flashed message from the session and to display it to the user,
    the template has to call :func:`get_flashed_messages`.

    .. versionchanged:: 0.3
       `category` parameter added.

    :param message: the message to be flashed.
    :param category: the category for the message.  The following values
                     are recommended: ``'message'`` for any kind of message,
                     ``'error'`` for errors, ``'info'`` for information
                     messages and ``'warning'`` for warnings.  However any
                     kind of string can be used as category.
    """
    # Original implementation:
    #
    #     session.setdefault('_flashes', []).append((category, message))
    #
    # This assumed that changes made to mutable structures in the session are
    # are always in sync with the session object, which is not true for session
    # implementations that use external storage for keeping their keys/values.
    flashes = session.get('_flashes', [])
    flashes.append((category, message))
    session['_flashes'] = flashes

    # ############### 触发 message_flashed 信号 ###############
    message_flashed.send(current_app._get_current_object(),
                         message=message, category=category)

message_flashed

message_flashed源码

def flash(message, category='message'):
    """Flashes a message to the next request.  In order to remove the
    flashed message from the session and to display it to the user,
    the template has to call :func:`get_flashed_messages`.

    .. versionchanged:: 0.3
       `category` parameter added.

    :param message: the message to be flashed.
    :param category: the category for the message.  The following values
                     are recommended: ``'message'`` for any kind of message,
                     ``'error'`` for errors, ``'info'`` for information
                     messages and ``'warning'`` for warnings.  However any
                     kind of string can be used as category.
    """
    # Original implementation:
    #
    #     session.setdefault('_flashes', []).append((category, message))
    #
    # This assumed that changes made to mutable structures in the session are
    # are always in sync with the session object, which is not true for session
    # implementations that use external storage for keeping their keys/values.
    flashes = session.get('_flashes', [])
    flashes.append((category, message))
    session['_flashes'] = flashes

    # ############### 触发 message_flashed 信号 ###############
    message_flashed.send(current_app._get_current_object(),
                         message=message, category=category)
message_flashed

 

四.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}