isaacclinton/python_bloc

Python bloc pattern framework that helps separation of business logic from presentation. Inspired by "dart bloc" library

Python implementation for the bloc pattern

Motivation

The project is motivated by dart's bloc library. Bloc design pattern helps to separate presentation from business logic.

Main features

Bloc

A bloc relies on events to trigger states i.e a bloc receives events and convert the incoming events into outgoing states

BlocObserver

A bloc observer listens to state changes of a bloc and it is intended to influence the presentation layer

State

Contains information of how the presentation layer looks like

Event

Triggers the bloc which in turn provides new states

Example 1 - Counter Bloc

Bloc

from bloc import Bloc
from enum import Enum


class Events(Enum):
    increment = 0
    decrement = 1


class CounterBloc(Bloc):

    def __init__(self) -> None:
        super().__init__(0)
        self.on(Events.increment, self.__increment)
        self.on(Events.decrement, self.__decrement)

    def __increment(self, event, emit):
        emit(self.current_state() + 1)

    def __decrement(self, event, emit):
        emit(self.current_state() - 1)

Testing

from bloc import bloc_test

def act(bloc):
    bloc.add(Events.increment)
    bloc.add(Events.increment)
    bloc.add(Events.decrement)

bloc_test(
    "Counter test",
    bloc=CounterBloc(),
    act=act,
    expect=[1, 2, 1],
)

Adding Observers

from bloc import BlocObserver

class MyObserver(BlocObserver):

    def on_change(self, old_state, new_state):
        print(f"MyObserver: old_state: {old_state} new_state: {new_state}")        


bloc = CounterBloc()
bloc.set_observer(MyObserver())
bloc.add(Events.increment)
bloc.add(Events.decrement)

output

MyObserver: old_state: 0 new_state: 1
MyObserver: old_state: 1 new_state: 0