Can you name and describe the patterns from the GoF book that you have used in your work projects?

The book "Design Patterns: Elements of Reusable Object-Oriented Software" (GoF) describes 23 classic design patterns. In practical Python projects, the following are often used:

• Singleton — ensures that a class has only one instance. In Python, it can be implemented via a module or a class with control over instance creation.

• Factory Method — defines an interface for creating an object, allowing subclasses to alter the type of objects that will be created.

• Observer — allows objects to subscribe to events of another object and receive notifications about changes.

• Decorator — dynamically adds new responsibilities to objects by wrapping them.

Example of using the Singleton pattern in Python:

class Singleton:
    _instance = None

    def __new__(cls):
        if cls._instance is None:
            cls._instance = super().__new__(cls)
        return cls._instance

s1 = Singleton()
s2 = Singleton()
print(s1 is s2)  # True

These patterns help write flexible and maintainable code.