Python @property decorator

In Python, the @property decorator is a convenient way to create a getter method for a class attribute. It allows us to define a method that is called when we access the attribute, as if it were a normal attribute, without explicitly calling the method.

Here’s an example of how the @property decorator can be used to create a getter for a class attribute:

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

    @property
    def radius(self):
        return self._radius
    
    @radius.setter
    def radius(self, value):
        if value < 0:
            raise ValueError("Radius must be non-negative")
        self._radius = value
    
    @property
    def diameter(self):
        return self._radius * 2
    
    @diameter.setter
    def diameter(self, value):
        if value < 0:
            raise ValueError("Diameter must be non-negative")
        self._radius = value / 2
    
    @property
    def area(self):
        return 3.14 * self._radius ** 2

c = Circle(5)
print(c.radius)    # 5
print(c.diameter)  # 10
print(c.area)      # 78.5
c.radius = 7
print(c.diameter)  # 14
print(c.area)      # 153.86
c.diameter = 20    # Sets radius to 10
print(c.radius)    # 10
print(c.area)      # 314.0
c.radius = -1      # ValueError: Radius must be non-negative

In this example, we define a Circle class with a radius attribute, and three methods that calculate the diameter, area, and validate the user input for radius attribute. We use the @property decorator to define getter methods for the radius, diameter, and area attributes.

We also use the @<attribute_name>.setter decorator to define setter methods for the radius and diameter attributes. The setter methods validate the user input for the radius and diameter attributes, and update the radius attribute accordingly.

When we create a Circle object c with a radius of 5, we can use the radius, diameter, and area attributes to get the corresponding values. The @property decorator allows us to define a simple and intuitive interface for working with the Circle object, without explicitly calling the getter methods.

When we set the radius or diameter attributes, the corresponding setter methods are called to validate the user input and update the radius attribute accordingly.

Using the @property decorator can be a useful way to define a simple and intuitive interface for working with class attributes, especially when the attributes require custom logic for access and modification.