Python property() Function

The property() function in Python is used to create managed attributes in object-oriented programming. It lets you define methods that act like attributes – helpful for adding logic when accessing or updating a value.

Syntax

property(fget=None, fset=None, fdel=None, doc=None)

Parameters:

• fget – Function to get the value (getter)
• fset – Function to set the value (setter)
• fdel – Function to delete the value (deleter)
• doc – Optional docstring

Returns:

• A property object that can be assigned to a class attribute

Example: Basic Usage of property()

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

    def get_name(self):
        print("Getting name...")
        return self._name

    def set_name(self, value):
        print("Setting name...")
        self._name = value

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

    name = property(get_name, set_name, del_name)

Usage:

p = Person("Alice")
print(p.name)      # Getting name... → Alice
p.name = "Bob"     # Setting name...
print(p.name)      # Getting name... → Bob
del p.name         # Deleting name...

Modern Alternative: Using @property Decorator

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

    @property
    def name(self):
        print("Getting name...")
        return self._name

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

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

Getting name...
Setting name...
Deleting name...

Why Use property()?

• Encapsulation: Control how attributes are accessed or modified
• Cleaner syntax: Looks like direct attribute access
• Backward compatibility: Add logic without changing the API

Common Mistakes

• Not using the underscore convention (e.g., _name) for internal variables
• Using property() without defining fget – it won’t be readable
• Using property incorrectly inside __init__

Interview Tip

Interviewers often ask about encapsulation and data hiding. Showing that you know how to use property and @property in Python can demonstrate your grasp of object-oriented principles.

Summary

• property() lets you control access to attributes in classes.
• You can use fget, fset, fdel to manage how values are accessed, set, or deleted.
• The @property decorator is a modern and cleaner alternative.

Practice Problem

Create a class Temperature with a Celsius attribute. Use @property to add a computed Fahrenheit property (read-only).

class Temperature:
    def __init__(self, celsius):
        self._celsius = celsius

    @property
    def fahrenheit(self):
        return (self._celsius * 9/5) + 32

t = Temperature(25)
print(t.fahrenheit)  # Output: 77.0