python-notify 1.0.1

Implementation of observer design pattern in python3

python-notify

python-notify is an object-oriented implementation of the observer design pattern in python3 supporting signature checking at connection stage, checking of passed arguments at call stage, notifiable collections as List, Dict and decorator @notifiable_property

Setup

Library can be installed with pip:

pip3 install python-notify

Simple examples

Signal

import typing

from notify.signal import Signal


class Obj:
    event_happened = Signal(data=typing.Mapping)


def event_handler(data: typing.Mapping):
    print(f'{data=}')

obj = Obj()
obj.event_happened.connect(event_handler)
obj.event_happened.notify({'key': 'value'})  # Will print "data={'key': 'value'}"

Collections

This package implements specialized container data types providing alternatives to Python's general purpose built-in containers, dict, list, with signals for state changes.

List signals

    items_added = Signal(items=typing.Tuple[object], pos=Position)
    items_changed = Signal(past_items=typing.Tuple[object], new_items=typing.Tuple[object], pos=Position)
    items_removed = Signal(items=typing.Tuple[object], pos=Position)
    items_cleared = Signal()

    # Where Position = t.Union[int, slice]

List example

import typing as t

from notify.collections import List


def on_items_added(items: t.Iterable[object], pos: int):
    print(items, pos)

obj = List((1, 2, 3))
obj.items_added.connect(on_items_added)

obj.extend((4, 5))
# will print: (4, 5), 3

Dict signals:

    key_added = Signal(key=object, item=object)
    key_changed = Signal(key=object, past_item=object, new_item=object)
    key_removed = Signal(key=object)

@notifiable_property

notifiable_property decorator is alternative to Python's @property decorator with signals for state changes.

from notify.property import notifiable_property


class Obj:
    def __init__(self, value):
        self._value = None
        self.value = value

    @notifiable_property
    def value(self):
        return self._value

    @value.setter
    def value(self, value):
        self._value = value * 2

    @value.deleter
    def value(self):
        del self._value


obj = Obj(value=1)
assert obj.value == 2


def on_value_changed(past_value, new_value):
    print(f'{past_value=}, {new_value=}')

obj.value_changed.connect(on_value_changed)

obj.value = 2
# Will print 'past_value=2, new_value=4'
assert obj.value == 4


def on_value_removed(past_value):
    print(f'{past_value=}')
obj.value_removed.connect(on_value_removed)

del obj.value
# Will print 'past_value=4'