python
class Singleton(type):
_instances = {}
def __call__(cls, *args, **kwargs):
if cls not in cls._instances:
cls._instances[cls] = super().__call__(*args, **kwargs)
return cls._instances[cls]
class MyClass(metaclass=Singleton):
pass
python
class Shape:
def draw(self):
pass
class Circle(Shape):
def draw(self):
print("Drawing a circle")
class Rectangle(Shape):
def draw(self):
print("Drawing a rectangle")
class ShapeFactory:
def create_shape(self, shape_type):
if shape_type == "circle":
return Circle()
elif shape_type == "rectangle":
return Rectangle()
else:
raise ValueError("Invalid shape type")
shape_factory = ShapeFactory()
circle = shape_factory.create_shape("circle")
circle.draw() # Output: Drawing a circle
python
from abc import ABC, abstractmethod
from typing import List, Any
class Observable:
def __init__(self):
self._observers = []
def add_observer(self, observer):
self._observers.append(observer)
def remove_observer(self, observer):
self._observers.remove(observer)
def notify_observers(self, data):
for observer in self._observers:
observer.update(data)
class Observer(ABC):
@abstractmethod
def update(self, data: Any):
pass
class TemperatureSensor(Observable):
def set_temperature(self, temperature):
self.notify_observers(temperature)
class Display(Observer):
def update(self, data):
print("Temperature:", data)
sensor = TemperatureSensor()
display = Display()
sensor.add_observer(display)
sensor.set_temperature(25) # Output: Temperature: 25
