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Added type hints to observer pattern #345

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Merged
faif merged 3 commits into from
Jul 23, 2020
Merged

Added type hints to observer pattern #345

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b4a65f8
Added type hints to observer pattern
rednafi Jul 23, 2020
27115a8
Updated signal links
rednafi Jul 23, 2020
daa2219
Handle unnamed exception with contextlib.suppress
rednafi Jul 23, 2020
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47 changes: 27 additions & 20 deletions patterns/behavioral/observer.py
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Original file line number Diff line number Diff line change
Expand Up @@ -5,57 +5,64 @@
Maintains a list of dependents and notifies them of any state changes.

*Examples in Python ecosystem:
Django Signals: https://docs.djangoproject.com/en/2.1/topics/signals/
Flask Signals: http://flask.pocoo.org/docs/1.0/signals/
Django Signals: https://docs.djangoproject.com/en/3.1/topics/signals/
Flask Signals: https://flask.palletsprojects.com/en/1.1.x/signals/
"""

from __future__ import annotations

from contextlib import suppress
from typing import List, Optional, Protocol


# define a generic observer type
class Observer(Protocol):
def update(self, subject: Subject) -> None:
pass


class Subject:
def __init__(self):
self._observers = []
def __init__(self) -> None:
self._observers: List[Observer] = []

def attach(self, observer):
def attach(self, observer: Observer) -> None:
if observer not in self._observers:
self._observers.append(observer)

def detach(self, observer):
try:
def detach(self, observer: Observer) -> None:
with suppress(ValueError):
self._observers.remove(observer)
except ValueError:
pass

def notify(self, modifier=None):
def notify(self, modifier: Optional[Observer] = None) -> None:
for observer in self._observers:
if modifier != observer:
observer.update(self)


class Data(Subject):
def __init__(self, name=""):
Subject.__init__(self)
def __init__(self, name: str = "") -> None:
super().__init__()
self.name = name
self._data = 0

@property
def data(self):
def data(self) -> int:
return self._data

@data.setter
def data(self, value):
def data(self, value: int) -> None:
self._data = value
self.notify()


class HexViewer:
def update(self, subject):
print(
"HexViewer: Subject {} has data 0x{:x}".format(subject.name, subject.data)
)
def update(self, subject: Data) -> None:
print(f"HexViewer: Subject {subject.name} has data 0x{subject.data:x}")


class DecimalViewer:
def update(self, subject):
print("DecimalViewer: Subject %s has data %d" % (subject.name, subject.data))
def update(self, subject: Data) -> None:
print(f"DecimalViewer: Subject {subject.name} has data {subject.data}")


def main():
Expand Down