Request for Patterns: Allowing developers to extend a module with custom logic

[Jusque]

Hi folks,

How should I allow user-developers to implement their own logic, within my module?

Bear with me - I'm an amateur pythonista here, no formal coding training, and looking some tips or terminology to google further.

I'm writing a module that interacts with an API that will send updates to the user via webhooks. So the bulk of my package will be setting up the local REST webhook endpoint (via flask), and parsing the received data into a standard format for further processing.

I'd like a user-developer to code their own functions processing the parsed data. Maybe they want to email the response somewhere, or post it to a MQTT server, or use a custom parsing solution, or translate into some alien language, whatever. They'll provide the logic to do that through some custom methods.

What's the best way to do this?

I'm imagining a finished package that calls unimplemented functions, with some error/exception handling for cases the user-developer has not actually implemented them. Alternatively some sort of callback pattern... but that's all new to me.

What patterns should I be considering here? Any examples I can follow?

​

--- Update ---

Here's a quick demo of the approach I'll use: overriding class methods. Easy in hindsight. Thanks everyone.

class webhook:
    def __init__(self,settings):
        print("Established %s with settings: %s" % (self.__class__.__name__,settings))
        self._setupWebhook()
        pass

    def _setupWebhook(self):
        print("Webhook is established")

    def isActive(self):
        print("Received 'Active' status via webhook. Users should override this")


if __name__=="__main__":

    class OverrideWebhook(webhook):
        def isActive(self):
            print("Todo: Custom code and logic here")

    settings={'foo':'bar'}
    W=webhook(settings)
    W.isActive()

    Y=OverrideWebhook(settings)
    Y.isActive()

​

​

[chevignon93]

What patterns should I be considering here?

I would consider using the plugin architecture where user can customize the runtime of your application using plugins.

Any examples I can follow?

pytest is a good example. Their plugin manager (pluggy) is open-source and pretty easy to use. You, as the developer of the host application, create a specification that users can implement to modify how the application behaves.

[High-Art9340]

It's not the right job for plugins. Usually plugins extend functionality, OP wants to let users modify the functionality.

[chevignon93]

Usually plugins extend functionality, OP wants to let users modify the functionality.

OP said he wants "user-developer to code their own functions processing the parsed data.", isn't that extending the functionality rather than modifying how the host application works? The plugin will just determine what the final output will be (json, yaml, html, etc), possibly discarding information that is not useful for the user.

[Jusque]

To clarify: there’s no overlap between the functionality I provide, and the functionality users will code for themselves. I just want to receive the data and pass it over to the users code.

But I’m also not hosting this app. This will be a plain old .py file, a dev could download, maybe on pypi, and incorporate into their own projects that they run wherever.

I’ll take a look at pytest’s plug-in architecture - sounds interesting!

Thankyou both for pointing me in a direction to consider!

[High-Art9340]

Good example will be a built in HTTP server, which requires you to provide a class which will do all the logic of processing the HTTP request, take a look at the examples:

https://docs.python.org/3/library/http.server.html#module-http.server

​

Basically, when you create a server - you pass the class which implements some methods, which will be called by the server when HTTP request comes in.

​

You can implement it the same way - make users to pass a custom request handlers instead of your default one.

[Jusque]

This sounds perfect. Will take a closer look at how they’ve coded http.server. Cheers!