What is the cached_property decorator module in Python?

The functools module in Python

The functools module in Python is used to create higher-order functions that interact with other functions. The higher-order functions either return other functions or operate on them to broaden the scope of the function without modifying or explicitly defining them.

The cached_property decorator

cached_property is a decorator that converts a class method into a property whose value is calculated once and then cached like a regular attribute. The cached value will be available until the object or the instance of the class is destroyed.

Syntax

@cached_property

Parameters

The decorator has no parameters.

Code

from functools import cached_property, reduce
class ListProduct:
    lst = []
    def __init__(self):
        self.lst = [1, 2, 3, 4, 6, 9]
    
    def product(self):
        print("product() method called.")
        return reduce(lambda x, y: x * y, self.lst)
    @cached_property
    def product_of_elements(self):
        print("product_of_elements() method called.")
        return reduce(lambda x, y: x * y, self.lst)
ListProductObject = ListProduct()
product = ListProductObject.product()
print("Product without caching - ", product)
print("--"*5)
product = ListProductObject.product()
print("Product without caching - ", product)
print("--"*5)
product = ListProductObject.product_of_elements
print("Product with caching - ", product)
print("--"*5)
product = ListProductObject.product_of_elements
print("Product with caching - ", product)

Explanation

  • Line 1: We import relevant methods and decorator from functools package.

  • Lines 3–16: We define a class called ListProduct that has two methods called product and product_of_elements. Both methods calculate the product of the elements in lst. product_of_elements method is decorated with @cached_property decorator.

  • Line 19: We create an instance of ListProduct class called ListProductObject.

  • Lines 20 to 26: The product is invoked on ListProductObject two times. Every time the method is invoked, the product of the elements in lst is calculated. We can verify this by checking whether the print statement in the product method is executed every time the method is called.

  • Lines 28 to 33: We invoke the product_of_elements on ListProductObject as a property two times. The first time the property is accessed, the product_of_elements() method is executed. The next time the same property is accessed, the cached value is served. We can verify this by checking whether the print statement in the product_of_elements method is executed every time the method is called.

Note: Refer How to use the reduce() method in Python to learn more about the reduce method.

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