Descriptors

Introduction

Descriptors provide a way to customize attribute access with getter, setter, and deleter methods.

Data Descriptor

class Descriptor:
    def __get__(self, obj, objtype=None):
        print(f"Getting: {obj}")
        return obj.__dict__.get('_value', 0)
    
    def __set__(self, obj, value):
        print(f"Setting: {value}")
        obj.__dict__['_value'] = value
    
    def __delete__(self, obj):
        print("Deleting")
        del obj.__dict__['_value']

class MyClass:
    attribute = Descriptor()

Property as Descriptor

class Circle:
    def __init__(self, radius):
        self.radius = radius
    
    @property
    def diameter(self):
        return self.radius * 2
    
    @diameter.setter
    def diameter(self, value):
        self.radius = value / 2

Function vs Method

class MyClass:
    def method(self):
        pass  # Function becomes bound method

# Bound method
obj = MyClass()
print(obj.method)  # <bound method MyClass.method of <MyClass>>

Practice Problems

1. Create descriptor with validation
2. Implement lazy loading descriptor
3. Create read-only descriptor
4. Build computed property descriptor
5. Use descriptor for unit conversion