Can you list the main principles of object-oriented programming?

Object-Oriented Programming (OOP) principles:

1. Encapsulation — combining data and methods that operate on that data into a single object, as well as hiding the internal implementation from the outside world.

2. Inheritance — a mechanism that allows creating new classes based on existing ones, inheriting their properties and methods.

3. Polymorphism — the ability of objects of different classes to respond to the same messages (method calls) in different ways.

4. Abstraction — highlighting the essential characteristics of an object, hiding implementation details.

Example in Python:

class Animal:
    def speak(self):
        pass

class Dog(Animal):
    def speak(self):
        return "Woof"

class Cat(Animal):
    def speak(self):
        return "Meow"

animals = [Dog(), Cat()]
for animal in animals:
    print(animal.speak())  # Polymorphism