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字段操作第三张表（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.core.signals import request_started
  from django.core.signals import got_request_exception

  from django.db.models.signals import class_prepared
  from django.db.models.signals import pre_init, post_init
  from django.db.models.signals import pre_save, post_save
  from django.db.models.signals import pre_delete, post_delete
  from django.db.models.signals import m2m_changed
  from django.db.models.signals import pre_migrate, post_migrate

  from django.test.signals import setting_changed
  from django.test.signals import template_rendered

  from django.db.backends.signals import connection_created


  def callback(sender, **kwargs):
    print("xxoo_callback")
    print(sender,kwargs)

  xxoo.connect(callback)
  # xxoo指上述导入的内容

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)

from django.db.models import signals

def before_save1(*args,**kwargs):
  print('有车来了，我要服务了--》',args,kwargs)

def before_save2(*args,**kwargs):
  print('有车来了，我要服务了--》',args,kwargs)

def after_save1(*args,**kwargs):
  print('有车来了，完事了--》',args,kwargs)

# 增加之前
signals.pre_save.connect(before_save1)
signals.pre_save.connect(before_save2)
# 增加之后
signals.post_save.connect(after_save1)

django_signals/__init__.py