Chapter 5. Using the API

AMQ Python is an asynchronous event-driven API. To define how an application handles events, the user implements callback methods on the MessagingHandler class. These methods are then called as network activity or timers trigger new events.

class ExampleHandler(MessagingHandler):
    def on_start(self, event):
        print("The container event loop has started")

    def on_sendable(self, event):
        print("A message can be sent")

    def on_message(self, event):
        print("A message is received")

These are only a few common-case events. The full set is documented in the API reference.

The event argument has attributes for accessing the object the event is regarding. For example, the on_connection_opened event sets the event connection attribute.

In addition to the primary object for the event, all objects that form the context for the event are set as well. Attributes with no relevance to a particular event are null.

event.container
event.connection
event.session
event.sender
event.receiver
event.delivery
event.message

The container is the top-level API object. It is the entry point for creating connections, and it is responsible for running the main event loop. It is often constructed with a global event handler.

handler = ExampleHandler()
container = Container(handler)
container.run()

Each container instance has a unique identity called the container ID. When AMQ Python makes a connection, it sends the container ID to the remote peer. To set the container ID, pass it to the Container constructor.

container = Container(handler)
container.container_id = "job-processor-3"

If the user does not set the ID, the library will generate a UUID when the container is constucted.