propertydecorator.md

The @property Decorator

Introduction

See also https://docs.python.org/3/library/functions.html#property

The property is a built-in Python function.

The @property decorator in Python is used to define getter methods in a class, allowing attribute access to be controlled without breaking encapsulation. It enables us to define a method that can be accessed like an attribute, making the code more readable and maintainable.

Why Use @property?

• Encapsulation: Protects class attributes from direct modification while allowing controlled access.
• Readability: Allows method calls to look like attribute access.
• Dynamic Properties: Computes values dynamically without changing the interface.

Basic Example

class Person:
    def __init__(self, name, age):
        self._name = name
        self._age = age

    @property
    def age(self):
        return self._age

p = Person("Alice", 30)
print(p.age)  # Accesses the method like an attribute

30

Using @property with Setter and Deleter

Adding a Setter

We can define a setter method using @<property_name>.setter to allow modification of the property.

class Person:
    def __init__(self, name, age):
        self._name = name
        self._age = age

    @property
    def age(self):
        return self._age

    @age.setter
    def age(self, value):
        if value < 0:
            raise ValueError("Age cannot be negative")
        self._age = value

p = Person("Alice", 30)
p.age = 35  # Updates age
print(p.age)  # Output: 35

35

Adding a Deleter

We can also define a deleter method using @<property_name>.deleter.

class Person:
    def __init__(self, name, age):
        self._name = name
        self._age = age

    @property
    def age(self):
        return self._age

    @age.deleter
    def age(self):
        print("Deleting age...")
        del self._age

p = Person("Alice", 30)
del p.age  # Calls the deleter

Deleting age...

Read-Only Property

If we only define the @property method and do not include a setter, the attribute becomes read-only.

class Circle:
    def __init__(self, radius):
        self._radius = radius

    @property
    def radius(self):
        return self._radius

c = Circle(5)
print(c.radius)  # Allowed
# c.radius = 10  # Raises AttributeError

5

Computed Properties

@property can be used to compute values dynamically.

class Rectangle:
    def __init__(self, width, height):
        self.width = width
        self.height = height

    @property
    def area(self):
        return self.width * self.height

rect = Rectangle(4, 5)
print(rect.area)  # Output: 20

20

Summary

The @property decorator in Python is a powerful feature that enhances encapsulation, maintains a clean API, and allows computed properties.

It helps to write clean and maintainable code.