How to use Python Decorators – with example

What is a Python decorator?
Declaring our example code
Applying a Python decorator
Summary
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What is a Python decorator?

Python decorators allow us to change the behaviour of a function without permanently making changes to the syntax of that function. This simply means that we can use a decorator which is usually another function to modify the behaviour of a class or function.

This is largely possible because in Python functions are first-class citizens. Therefore this means that we can pass a function as a parameter to another function or return a function from another function.

In this article, we are going to use a really basic example to explore how we can create a decorator and how we can use it. This example also illustrates the concept of metaprogramming where a part of the program tries to modify another program at compile time.

Declaring our example code

So we will start off by creating a simple function that simply prints out a message when executed. We have named the function learn_to_code().

Modify the function

Now that we have our target function in place we wish to create a decorator that will try to modify the above function. We are going to create a function that will allow us to split the string returned by the learn_to_code() function into a list.

In order to achieve this, we are going to make use of the concept of higher-order functions and nesting. This means that we will create a function that takes another function as an argument.

We are going to name this function split_string(), which this the main function that accepts another function as an argument. Now within this function, we have also nested another function named the wrapper() function.

Using the wrapper function

Now within the wrapper function, we have assigned the output from the function passed as an argument to the split_string() function to a variable named func. Finally, we have made use of the built-in split() function to split the string that will be returned by the learn_to_code() function into a list.

def split_string(function):
    def wrapper():
        func = function()
        str_list = func.split()
        return str_list
       
    return wrapper

The split function normally accepts two optional parameters, a separator and a max split that specifies the number of splits to be performed.

string.split(separator, maxsplit)

However, when the two parameters are not specified the interpreter will by default use the whitespace as the separator and a default value of ‘-1’ as the maxsplit.

Applying a Python decorator

Now to apply this decorator function to the function we created earlier we will make use of the @ symbol followed by the name of the decorator function as shown below. Now when we run the code below we will get the string returned by the learn_to_code() function split into a list.

Applying a Python Decorator to Multiple Functions

We can also apply a single decorator to multiple functions improving code reusability in the process. To demonstrate this concept we will create another function that returns the names of animals.

Using Python decorators with the @ symbol

In a similar manner, we can also apply the Python decorators function that we created earlier on to this function using the @ symbol and the name of the decorator function.

Summary

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