Model signals
  pre_init          # django的modal执行其构造方法前，自动触发
  post_init          # django的modal执行其构造方法后，自动触发
  pre_save          # django的modal对象保存前，自动触发
  post_save          # django的modal对象保存后，自动触发
  pre_delete         # django的modal对象删除前，自动触发
  post_delete         # django的modal对象删除后，自动触发
  m2m_changed         # django的modal中使用m2m字段操作第三张（add,remove,clear）前后，自动触发
  class_prepared       # 程序启动时，检测已注册的app中modal类，对于每一个类，自动触发
  
Management signals
  pre_migrate         # 执行migrate命令前，自动触发
  post_migrate        # 执行migrate命令后，自动触发
  
Request/response signals
  request_started       # 请求到来前，自动触发
  request_finished      # 请求结束后，自动触发
  got_request_exception    # 请求异常后，自动触发
  
Test signals
  setting_changed       # 使用test测试修改配置文件时，自动触发
  template_rendered      # 使用test测试渲染模板时，自动触发
  
Database Wrappers
  connection_created     # 创建数据库连接时，自动触发

from django.core.signals import request_finished
from django.dispatch import receiver

@receiver(request_finished)
def my_callback(sender, **kwargs):
  print("Request finished!")

import django.dispatch
pizza_done = django.dispatch.Signal(providing_args=["toppings", "size"])

def callback(sender, **kwargs):
  print("callback")
  print(sender,kwargs)
  pizza_done.connect(callback) 

from 路径 import pizza_done
pizza_done.send(sender='seven',toppings=123, size=456)

# coding:utf-8
from django.dispatch import Signal
post_update = Signal(providing_args=["user"])

//引入自定义的signal文件
from tools import signals 

class MyCustomQuerySet(models.query.QuerySet):
  def update(self, **kwargs):
    super(MyCustomQuerySet, self).update(**kwargs)
    //update被调用时， 发送该singalsignals
    signals.post_update.send(sender=self.model, user="xxx")
    print("finished!")

class MyCustomManager(models.Manager):
  def get_queryset(self):
    return MyCustomQuerySet(self.model, using=self._db)

class crontab_ping(models.Model):
  name = models.CharField(max_length=64, blank=True, null=True)
  objects = MyCustomManager()

from tools.signals import post_update

@receiver(post_update)
def post_update_callback(sender, **kwargs):
  print(kwargs['user'])
  print("post_update_success")