pgnotifpy

A Simple wrapper around psycopg2 to handle PostgreSQL NOTIFY à la Flask

pgnotifpy is a simple wrapper around psycopg2 to work with PostgreSQL notification with a Flask-like API:

import pgnotifpy

li = pgnotifpy.Listener('dbname', 'user')

@li.listen('new_user')
def say_hello(data):
    print('hi', data)

@li.listen('delete_user')
def say_bye(data):
    print('bye', data)

li.run('job', dispatch)

This code will listen for events originating from a NOTIFY 'job', <DATA> query.

pgnotifpy allows you to use your own dispatcher, so you are not obliged to follow a specific convention for your messages.

For example, suppose you work with JSON-encoded messages that looks like this:

{
    "action": "new_user",
    "data": {
        "id": 42,
        "name": "John Doe"
    }
}

All you have to do is to write a simple dispatcher function so pgnotifpy can do the correct routing for you.

def my_dispatch(payload):
    try:
        data = json.loads(payload)
        action = data['action']
        message = data.get('data')
    except (ValueError, KeyError):
        print('Ill-formed JSON message :(')
        return
    return action, message

Then, just pass it to the run method:

li.run('job', my_dispatcher)

A dispatcher function is expected to have the following signature:

dispatcher(payload: str) -> Option[Tuple[str, any]]

That is, if a dispatcher returns ('new_user', data), all functions listening to 'new_user' will be triggered with data supplied as the only argument.

FAQ

Is it ready for production?

Short answer: Not yet.

Long &nswer: I use this wrapper in some real projects. However, this wrapper is used in specific environments that does not allow edge-cases such as an unexpectedly disconnected database.

Is it asynchronous?

No.

This library is a wrapper over psycopg2 which works in a synchronous manner. Maybe someday I will make a version using the asyncpg library which supports async.

Use cases

This library may not be suited for high-throughput processing such as data streaming. But, would you use PostgreSQL's NOTIFY/LISTEN for this kind of task anyway? :)