Daily Archives: October 14, 2021

General

Decorator Pattern

import abc
class Shape(abc.ABC):
    @abc.abstractmethod
    def draw(self):
        pass

class Triangle(Shape):
    def draw(self):
        print("Triangle")

class Circle(Shape):
    def draw(self):
        print("Circle")

# Decorator was not needed to be inherited from Shape in Python.But you can enforce the draw function
# In Java, inheritance forces to implement parent methods to child Decorators.
class Decorator(Shape):
    def __init__(self, shape):
        self.shape = shape

class ColorDecorator(Decorator):
    def __init__(self, shape, color):
        super().__init__(shape)
        self.color = color

    def draw(self):
        print(self.color)
        self.shape.draw()
        print(self.color)

class PatternDecorator(Decorator):
    def __init__(self, shape, pattern):
        super().__init__(shape)
        self.pattern = pattern

    def draw(self):
        print(self.pattern)
        self.shape.draw()
        print(self.pattern)

s = Circle()
s.draw()
cd = ColorDecorator(s, "red")
cd.draw()
pd = PatternDecorator(Triangle(), "Polca dot")
pd.draw()
redPolcaDorCircle = PatternDecorator(cd, "Polca dot")
redPolcaDorCircle.draw()
General

State Pattern

# Allowing an object to alter behavior
# when its internal state changes so that it appears to change its class

class Phone:
    def __init__(self):
        self.ring_state = SoundState()
    def volumeUp(self):
        self.ring_state = self.ring_state.nextVolumeUp()
    def volumeDown(self):
        self.ring_state = self.ring_state.nextVolumeDown()
    def ring(self):
        self.ring_state.ring()

import abc

class RingState(abc.ABC):
    @abc.abstractmethod
    def ring(self):
        pass
    @abc.abstractmethod
    def nextVolumeUp(self):
        pass
    @abc.abstractmethod
    def nextVolumeDown(self):
        pass

class SoundState(RingState):
    def ring(self):
        print("Phone is ringing")
    def nextVolumeUp(self):
        return self
    def nextVolumeDown(self):
        return VibrateState()

class VibrateState(RingState):
    def ring(self):
        print("Phone is vibrating")
    def nextVolumeUp(self):
        return SoundState()
    def nextVolumeDown(self):
        return SilentState()

class SilentState(RingState):
    def ring(self):
        print("Phone is silent")
    def nextVolumeUp(self):
        return VibrateState()
    def nextVolumeDown(self):
        return self

phone = Phone()
phone.ring()
phone.volumeDown()
phone.ring()
phone.volumeDown()
phone.ring()
phone.volumeDown()
phone.ring()
phone.volumeUp()
phone.ring()
phone.volumeUp()
phone.ring()
General

Strategy Pattern

class File:
    def __init__(self):
        self.strategy = None

    def compress(self):
        self.strategy.compress()

import abc
class CompressionStrategy(abc.ABC):
    @abc.abstractmethod
    def compress(cls):
        pass

class ZipCompression(CompressionStrategy):
    def compress(cls):
        print("zip Compression")

class RarCompression(CompressionStrategy):
    def compress(cls):
        print("rar Compression")

f = File()
f.strategy = ZipCompression()
f.compress()

f.strategy = RarCompression()
f.compress()