This library provides a mechanism for forms (and other components) within an Anvil app to communicate in a ‘fire and forget’ manner.

It’s an alternative to raising and handling events - instead you ‘publish’ messages to a channel and, from anywhere else, you subscribe to that channel and process those messages as required.


Create the Publisher

You will need to create an instance of the Publisher class somewhere in your application that is loaded at startup.

For example, you might create a client module at the top level of your app called ‘common’ with the following content:

from anvil_extras.messaging import Publisher

publisher = Publisher()

and then import that module in your app’s startup module/form.

Publish Messages

From anywhere in your app, you can import the publisher and publish messages to a channel. e.g. Let’s create a simple form that publishes a ‘hello world’ message when it’s initiated:

from ._anvil_designer import MyPublishingFormTemplate
from .common import publisher

class MyPublishingForm(MyPublishingFormTemplate):

    def __init__(self, **properties):
        publisher.publish(channel="general", title="Hello world")

The publish method also has an optional ‘content’ parameter which can be passed any object.

Subscribe to a Channel

Also, from anywhere in your app, you can subscribe to a channel on the publisher by providing a handler function to process the incoming messages.

The handler will be passed a Message object, which has the title and content of the message as attributes.

e.g. On a separate form, let’s subscribe to the ‘general’ channel and print any ‘Hello world’ messages:

from ._anvil_designer import MySubscribingFormTemplate
from .common import publisher

class MySubscribingForm(MySubscribingFormTemplate):

    def __init__(self, **properties):
            channel="general", subscriber=self, handler=self.general_messages_handler

    def general_messages_handler(self, message):
        if message.title == "Hello world":

You can unsubscribe from a channel using the publisher’s unsubscribe method.

You can also remove an entire channel using the publisher’s close_channel method.

Be sure to do one of these if you remove instances of a form as the publisher will hold references to those instances and the handlers will continue to be called.


By default, the publisher will log each message it receieves to your app’s logs (and the output pane if you’re in the IDE).

You can change this default behaviour when you first create your publisher instance:

from anvil_extras.messaging import Publisher
publisher = Publisher(with_logging=False)

The publish, subscribe, unsubscribe and close_channel methods each take an optional with_logging parameter which can be used to override the default behaviour.