Working With Signals.

Django includes a “signal dispatcher” which helps allow decoupled applications get notified when actions occur elsewhere in the framework. In a nutshell, signals allow certain senders to notify a set of receivers that some action has taken place. They’re especially useful when many pieces of code may be interested in the same events.

Django provides a set of built-in signals that let user code get notified by Django itself of certain actions. These include some useful notifications:

• django.db.models.signals.pre_save & django.db.models.signals.post_save
  Sent before or after a model’s save() method is called.
• django.db.models.signals.pre_delete & django.db.models.signals.post_delete
  Sent before or after a model’s delete() method or queryset’s delete() method is called.
• django.db.models.signals.m2m_changed
  Sent when a ManyToManyField on a model is changed.
• django.core.signals.request_started & django.core.signals.request_finished
  Sent when Django starts or finishes an HTTP request.

In this i am showing u step by step process for sucessful 

First step :

Create an Signals.py  file in the folder where u wan to add the signals to models

second step;

There will be an init.py file in  every folder of django .open it and type

import signals

third step open ur signals.py and add the following

# in models.py

from django.db.models.signals import post_save

from django.dispatch import receiver

// below example shows signal that is triggered after saving of model

@receiver(post_save, sender=< ur model name>)

def <function name>(sender, **kwargs):

    # the object which is saved can be accessed via kwargs 'instance' key.

    obj = kwargs['instance']

    print obj.username