Signals

BYCEPS makes use of signals (based on the Blinker package) to provide hooks for specific events.

For example, a signal is emitted every time

  • a user account is created
  • a topic in the board is created
  • an order is placed in the shop

Besides representing the information that something happened, signals can (and usually do) contain relevant objects as well.

To receive signals, handlers can be registered for those they are interested in.

Some specific knowledge is necessary to attach code to a specific signal and access its payload, though.

  • to import it: the module and name of the signal
  • to handle it: the types of the objects it contains, and the keyword argument names they can be accessed with

Example

As a simple example for learning purposes, here is the code to print a message to STDOUT (visible when manually starting the application from the command line, e.g. for development and debugging).

from byceps.blueprints.board.signals import topic_created

@topic_created.connect
def celebrate_created_topic(sender, *, topic=None):
    print('A topic entitled "{}" has been created.'.format(topic.title))

More useful reactions include:

  • announcing selected events via email, on IRC, or on social media sites
  • creating/assigning a party ticket once the corresponding order has been paid
  • running spam detection on new board topics and postings