Magic methods customise object behaviour. __repr__ defines the debug string, __str__ the display string, __len__ makes len() work, and __eq__ defines equality. They make your classes feel like built-in types.
Dunder / Magic Methods
class Vector:
def __init__(self, x, y):
self.x, self.y = x, y
def __repr__(self):
return f"Vector({self.x}, {self.y})"
def __add__(self, other):
return Vector(self.x+other.x, self.y+other.y)
def __len__(self):
return 2
v = Vector(1, 2) + Vector(3, 4)
print(v) # Vector(4, 6)
print(len(v)) # 2