Lære Introduction to Decorators | Mastering Python Decorators

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Definition

A decorator in Python is a higher-order function that takes another function as its argument and returns a new function that extends or alters the behavior of the original function.

Decorators are a core feature in Python that allow you to modify or enhance the behavior of functions or methods without changing their code directly. At their heart, decorators are higher-order functions — they take another function as an argument, extend or alter its behavior, and return a new function. In Python, the syntax for applying a decorator is the @ symbol followed by the decorator name, placed directly above the function definition.

Common use cases for decorators include:

Logging;
Timing how long functions take to run;
Enforcing access control or permissions;
Memoization (caching results);
Input validation.

Decorators let you keep such logic separate from your core business logic, leading to cleaner and more maintainable code. By mastering decorators, you unlock a powerful tool for writing reusable and expressive Python code.


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def simple_decorator(func):
    def wrapper(*args, **kwargs):
        print("Before the function call")
        result = func(*args, **kwargs)
        print("After the function call")
        return result
    return wrapper

@simple_decorator
def greet(name):
    print(f"Hello, {name}!")

greet("Alice")

Understanding *args and **kwargs in Function Definitions

When writing decorators and wrappers, you often need to handle functions that take any number or type of arguments. Python provides *args and **kwargs to make this possible.

*args collects any extra positional arguments passed to a function into a tuple;
**kwargs collects any extra keyword arguments into a dictionary.

This flexibility is crucial for decorators. A decorator must be able to accept and forward all arguments to the original function, no matter how many or what kind they are. Without *args and **kwargs, your decorator would only work with functions that have a fixed signature, limiting reusability.


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def my_decorator(func):
    def wrapper(*args, **kwargs):
        print("Arguments:", args)
        print("Keyword arguments:", kwargs)
        return func(*args, **kwargs)
    return wrapper

@my_decorator
def example(a, b, greeting="Hello"):
    print(f"{greeting}, {a} and {b}!")

example(1, 2, greeting="Hi")

This approach ensures your decorator can wrap any function, making your code both robust and reusable.

1. What is the purpose of the `@` symbol in Python?

2. How does a decorator modify a function's behavior?

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Introduction to Decorators

Understanding *args and **kwargs in Function Definitions

1. What is the purpose of the @ symbol in Python?

2. How does a decorator modify a function's behavior?

1. What is the purpose of the `@` symbol in Python?