Property Decorators in Python (@property, @setter, @deleter)

Property decorators allow you to control how class attributes are accessed, modified, and deleted while keeping a clean syntax.

They help you: - Protect data (encapsulation) - Add validation logic - Keep attribute-style access (obj.value) instead of method calls

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Why Property Decorators?

Without property:

obj.get_value()
obj.set_value(10)

With property:

obj.value
obj.value = 10

Cleaner, safer, more Pythonic.

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1. @property (Getter)

Used to access a method like an attribute.

Example:

class Student:
    def __init__(self, name):
        self._name = name

    @property
    def name(self):
        return self._name

s = Student("Aman")
print(s.name)

Output:

Aman

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Real World Example

Bank balance (read-only access):

class BankAccount:
    def __init__(self, balance):
        self._balance = balance

    @property
    def balance(self):
        return self._balance

acc = BankAccount(5000)
print(acc.balance)

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Graph (Flow)

obj.balance
     ↓
@property method runs
     ↓
returns value safely

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Common Mistake

class A:
    @property
    def value(self):
        return 10

a = A()
print(a.value())

Error: - property is not callable

Correct:

print(a.value)

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Homework 1

Create a class Product with a read-only price property.

Solution:

class Product:
    def __init__(self, price):
        self._price = price

    @property
    def price(self):
        return self._price

p = Product(100)
print(p.price)

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2. @setter (Setter)

Used to modify a property safely.

Example:

class Student:
    def __init__(self, name):
        self._name = name

    @property
    def name(self):
        return self._name

    @name.setter
    def name(self, value):
        self._name = value

s = Student("Aman")
s.name = "Ravi"
print(s.name)

Output:

Ravi

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Real World Example

User password validation:

class User:
    def __init__(self, password):
        self._password = password

    @property
    def password(self):
        return "****"

    @password.setter
    def password(self, value):
        if len(value) < 6:
            print("Weak password")
        else:
            self._password = value

u = User("123456")
u.password = "abc"

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Graph

obj.value = 10
      ↓
@setter validation runs
      ↓
value stored safely

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Common Mistake

class A:
    @property
    def x(self):
        return 10

    @x.setter
    def x(self, value):
        self.x = value

Problem: - infinite recursion

Correct:

self._x = value

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Homework 2

Create a class Employee with salary validation: - salary must be > 0

Solution:

class Employee:
    def __init__(self, salary):
        self._salary = salary

    @property
    def salary(self):
        return self._salary

    @salary.setter
    def salary(self, value):
        if value <= 0:
            print("Invalid salary")
        else:
            self._salary = value

e = Employee(1000)
e.salary = 2000
print(e.salary)

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3. @deleter (Delete Property)

Used to delete an attribute safely.

Example:

class Student:
    def __init__(self, name):
        self._name = name

    @property
    def name(self):
        return self._name

    @name.deleter
    def name(self):
        print("Deleting name")
        del self._name

s = Student("Aman")
del s.name

Output:

Deleting name

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Real World Example

Account deletion:

class Account:
    def __init__(self, user):
        self._user = user

    @property
    def user(self):
        return self._user

    @user.deleter
    def user(self):
        print("Account removed")
        del self._user

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Graph

del obj.value
      ↓
@deleter method runs
      ↓
cleanup happens

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Common Mistake

del obj.value()

Error: - property is not callable

Correct:

del obj.value

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Homework 3

Create a class File: - property name - allow deletion with message "File deleted"

Solution:

class File:
    def __init__(self, name):
        self._name = name

    @property
    def name(self):
        return self._name

    @name.deleter
    def name(self):
        print("File deleted")
        del self._name

f = File("data.txt")
del f.name

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Summary Table

Decorator	Purpose	Example
@property	getter	access value safely
@setter	modify value	validation logic
@deleter	delete value	cleanup

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Real World Mapping

Feature	Real Example
property	bank balance view
setter	password update
deleter	account deletion

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Property Flow Diagram

GET → @property
SET → @setter
DEL → @deleter

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Full Example (All Together)

class User:
    def __init__(self, name):
        self._name = name

    @property
    def name(self):
        return self._name

    @name.setter
    def name(self, value):
        self._name = value

    @name.deleter
    def name(self):
        del self._name

u = User("Aman")
print(u.name)
u.name = "Ravi"
del u.name

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Common Mistakes Summary

• Using function call on property (obj.name())
• Recursive setter (self.name = value)
• Forgetting underscore storage (self._name)

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Next Advanced Topics

• Descriptors in Python
• OOP Encapsulation deep dive
• Magic methods (__get__, __set__)
• Data Classes (@dataclass)
• Abstract Base Classes (ABC)
• Advanced OOP design patterns ```