What are magic methods (dunder methods)? Why are they called magic?

Magic methods in Python are special methods whose names start and end with double underscores (e.g., __init__, __str__, __add__). They are called "magic" because they allow changing the behavior of objects and classes at the language level, such as defining how an object is created, converted to a string, compared, or interacts with operators.

Example:

class Vector:
    def __init__(self, x, y):
        self.x = x
        self.y = y

    def __add__(self, other):
        return Vector(self.x + other.x, self.y + other.y)

    def __str__(self):
        return f"Vector({self.x}, {self.y})"

v1 = Vector(1, 2)
v2 = Vector(3, 4)
print(v1 + v2)  # Outputs: Vector(4, 6)

Here, __add__ allows using the + operator to add Vector objects, and __str__ outputs them in a readable format.