[![PyPI version](https://badge.fury.io/py/observ.svg)](https://badge.fury.io/py/observ) [![CI status](https://github.com/Korijn/observ/workflows/CI/badge.svg)](https://github.com/Korijn/observ/actions) # Observ ���� Observ is a Python port of [Vue.js](https://vuejs.org/)' [computed properties and watchers](https://vuejs.org/v2/guide/computed.html). It is completely event loop/framework agnostic and has no dependencies so it can be used in any project targeting Python >= 3.6. Observ provides the following two benefits for stateful applications: 1) You no longer need to manually invalidate and recompute state (e.g. by dirty flags): * computed state is invalidated automatically * computed state is lazily re-evaluated 2) You can react to changes in state (computed or not), enabling unidirectional flow: * _state changes_ lead to _view changes_ (e.g. a state change callback updates a UI widget) * the _view_ triggers _input events_ (e.g. a mouse event is triggered in the UI) * _input events_ lead to _state changes_ (e.g. a mouse event updates the state) ## API `from observ import observe, computed, watch` * `state = observe(state)` Observe nested structures of dicts, lists, tuples and sets. Returns an observable clone of the state input object. * `watcher = watch(func, callback, deep=False, immediate=False)` React to changes in the state accessed in `func` with `callback(old_value, new_value)`. Returns a watcher object. `del`elete it to disable the callback. * `wrapped_func = computed(func)` Define computed state based on observable state with `func` and recompute lazily. Returns a wrapped copy of the function which only recomputes the output if any of the state it depends on becomes dirty. Can be used as a function decorator. ## Quick start and example Install observ with pip/pipenv/poetry: `pip install observ` Check out [`examples/observe_qt.py`](https://github.com/Korijn/observ/blob/master/examples/observe_qt.py) for a simple example using observ.