gso

GSO (Global State Observer)

GSO is an open-source Python library for managing application state. It uses a modified version of the Observer pattern to sync UI state with application state.

GSO was originally designed to work with PySide/ PyQt, but it works well with pretty much every class-based UI library out there.

How to use

You will find a lot of examples that can help you get started. The examples are very simple, they are all focused on the pattern that works best with GSO.

You are encouraged to clone the ones that use the UI library you are working with and have a closer look.

Flow

In GSO, application state is encapsulated in observables.

An observable is like a wrapper around the actual state or variable.

All an observable brings to the table is that it keeps references to objects (usually UI components) that are interested in knowing when the wrapped state changes.

Observables force notification of observers when encapsulated state changes, so whenever application state changes, UI components can instantly update accordingly.

All UI components that depend on at least one variable in application state should implement the Observer interface, and each of these variables should be encapsulated in an Observable.

That was the O in GSO, the Observer pattern.

You might be thinking, how do UI components reach state? Well, that's where the GS comes to play.

The GlobalState class is used to group all application state variables and make them globally available everywhere in your code, so that UI components can easily request state updates and observe application state. It acts as a singleton, and stores all the observables in a Python dict.

As you already know, an observable can have multiple observers, and an observer can observe multiple observables.

In other words, one variable in application state can have multiple UI components depending on it, and one UI component can have it's state depend on multiple variables in application state, which is why the notify_state_changed() method on Observers accepts the parameter action.

If you are familiar with Redux, you probably already have an idea what actions are, they are pretty similar in GSO, but they are not the same.

In both Redux and GSO, actions are objects that describe what kind of update should take place in application state.

In Redux, every action has a unique name, and a payload that has all what is needed to make the corresponding update properly.

However, in GSO, actions are distinct objects that encapsulate state update logic. They are used by Observables in their apply() method to update encapsulated state using the encapsulated logic.

If you found any of this confusing or unclear, please refer to the examples.

How to install

Make sure you have pip installed, then open a terminal window, and type:

pip install gso