A django signal working flow

django_signal.py

from dispatch import Signal

# The Signal object (think of it as an exchange)
log_it = Signal(providing_args=['level', 'message'])

# These functions are receivers (subscribers). They will receive 
# the signal (message) sent (published) by the sender (publisher).
def simple_receiver(**kwargs):
    message, level = kwargs['message'], kwargs['level']
    print 'Receiver # 1'
    print '\tLevel: %d, Message: %s\n' % (level, message)

def picky_receiver(**kwargs):
    message, level = kwargs['message'], kwargs['level']
    print 'Receiver # 2'
    if level < 2:
        print "\tSome unimportant message was sent. Ignoring it!\n"

# Okay, now time to connect these receivers to the log_it signal object.
log_it.connect(simple_receiver)
log_it.connect(picky_receiver)

# The sender (publisher) that sends (publishes) a signal (message).
# This message will received by all connected (subscribed)
# receivers (subscribers).
def a_cool_sender():
    # Do something cool here
    # Now send a signal to all receivers
    log_it.send(sender='a_cool_sender', message='Hello!', level=1)
a_cool_sender()

Reference: http://www.shutupandship.com/2012/04/django-signals-and-observer-design.html

The signal creation and receiver callback is not that difficult to understand, but when sending a signal, the sender arguments in the Signal.send(sender, **kwargs) function can be either the instance of a class or the function name if it is called inside a function.