How to Use Property Decorator in Python: Simple Guide

In Python, the @property decorator lets you define methods that act like attributes, allowing controlled access to instance variables. You use @property for the getter method, and @.setter to define the setter method for the same attribute.

Syntax

The @property decorator is placed above a method to make it behave like a read-only attribute. To allow setting a value, you define a setter method with @property_name.setter. Optionally, you can add a deleter with @property_name.deleter.

• Getter: Method to get the attribute value.
• Setter: Method to set the attribute value.
• Deleter: Method to delete the attribute.

python

class MyClass:
    @property
    def attribute(self):
        # getter method
        return self._attribute

    @attribute.setter
    def attribute(self, value):
        # setter method
        self._attribute = value

    @attribute.deleter
    def attribute(self):
        # deleter method
        del self._attribute

Example

This example shows a class with a private variable _temperature and a property temperature that controls access to it. The setter checks that the temperature is not below absolute zero.

python

class Celsius:
    def __init__(self, temperature=0):
        self._temperature = temperature

    @property
    def temperature(self):
        return self._temperature

    @temperature.setter
    def temperature(self, value):
        if value < -273.15:
            raise ValueError("Temperature below -273.15 is not possible")
        self._temperature = value

c = Celsius()
c.temperature = 25
print(c.temperature)

try:
    c.temperature = -300
except ValueError as e:
    print(e)

Output

25
Temperature below -273.15 is not possible

Common Pitfalls

One common mistake is forgetting to use the @property decorator on the getter method, which means the attribute won't behave like a property. Another is not using the correct setter decorator name (@property_name.setter), causing errors. Also, directly accessing the private variable outside the class defeats the purpose of using properties.

python

class Wrong:
    def temperature(self):  # Missing @property
        return self._temperature

    def temperature(self, value):  # This does not set a property setter
        self._temperature = value

# Correct way:
class Right:
    @property
    def temperature(self):
        return self._temperature

    @temperature.setter
    def temperature(self, value):
        self._temperature = value

Quick Reference

Decorator	Purpose
@property	Defines the getter method to access the attribute.
@.setter	Defines the setter method to modify the attribute.
@.deleter	Defines the deleter method to delete the attribute.

Key Takeaways

Use @property to create a method that acts like a read-only attribute.

Define a setter with @property_name.setter to allow controlled attribute changes.

Always use a private variable (like _attribute) to store the actual data.

Forget not to decorate the getter method with @property or the property won't work.

Properties help encapsulate data and add validation easily.