Python Decorators: A Beginner-Friendly Introduction

This guide explains decorators: a beginner-friendly introduction through a focused Python example. You will learn the behavior to expect, why it matters in a real program, and how to recognize the common mistakes before applying it in your own project.

What You Will Learn

A decorator wraps or replaces a function with additional behavior. The @ syntax applies the decorator when the function is defined, while later calls use the decorated result.

When and Why to Use It

The following example focuses on a practical use of Decorators: A Beginner-Friendly Introduction.

Step-by-Step Example

def announce_call(function):
    def wrapper():
        print("Starting")
        return function()
    return wrapper

@announce_call
def say_hello():
    print("Hello")

say_hello()

Understanding the Example

Calling say_hello actually calls wrapper, which prints Starting and then invokes the original function. The original behavior remains available inside the closure.

Expected Output

Starting
Hello

Important Behavior and Edge Cases

This first example supports no function arguments. Production decorators usually forward *args and **kwargs and use functools.wraps.

Try It Yourself

Modify wrapper so that it also prints Finished after the original function returns.

Common Beginner Mistakes

• This first example supports no function arguments. Production decorators usually forward *args and **kwargs and use functools.wraps.
• Confusing a returned value with printed output, or failing to verify a function’s behavior with different input values.
• Skipping the practice step and assuming the example covers every input. Test at least one normal case and one edge case relevant to this topic.

Key Takeaways

• A decorator wraps or replaces a function with additional behavior.
• Calling say_hello actually calls wrapper, which prints Starting and then invokes the original function.
• Apply the technique deliberately, checking its documented input requirements and failure behavior before integrating it into a larger project.