How to Effectively Use and Chain Decorators in Python?

How to Make and Chain Decorators in Python

Creating Decorators

Write a decorator function that takes another function, called a "wrapped" function, as an argument:

def my_decorator(func):

    # Code to execute before calling the wrapped function
    print("Before the function runs")

    # Call the wrapped function and store its return value
    result = func()

    # Code to execute after calling the wrapped function
    print("After the function runs")

    # Return the result of the wrapped function
    return result

# Example of a decorator in action
@my_decorator
def say_hello():
    print("Hello, world!")

Chaining Decorators

Use the @ operator to apply multiple decorators to the same function:

@my_decorator
@another_decorator
def chained_function():
    print("This function is doubly decorated")

Decorators with Arguments

Allow decorators to accept arguments:

def decorator_with_arg(arg1, arg2):

    def decorator(func):

        # Use the decorator arguments to modify the wrapped function's behavior
        func.arg1 = arg1
        func.arg2 = arg2

        return func

# Example of a decorator with arguments
@decorator_with_arg("foo", "bar")
def my_function():
    print("Args:", my_function.arg1, my_function.arg2)

Decorators for Class Methods

Use decorators for methods in a class:

class MyClass:

    @classmethod
    def my_class_method(cls):
        print("This is a class method")

Practice: Decorating a Decorator

Create a decorator that makes any other decorator accept arguments:

def decorator_with_args(decorator_to_enhance):

    def decorator_maker(*args, **kwargs):

        def decorator_wrapper(func):

            # Wrap the original decorator and pass the arguments
            return decorator_to_enhance(func, *args, **kwargs)

        return decorator_wrapper


# Example of a decorated decorator
@decorator_with_args
def decorated_decorator(func, *args, **kwargs):
    print("Args:", args, kwargs)
    return func


@decorated_decorator(10, 20, name="John")
def my_function():
    print("Decorated function")

Best Practices

• Avoid slowing down code due to decorator overhead.
• Use functools.wraps() to preserve the original function's information.
• Decorators are permanent once applied to a function.
• Consider using them for debugging or extending existing functionality from external libraries.

Example Uses

Use decorators for tasks like:

• Measuring function execution time (@benchmark)
• Logging function calls (@logging)
• Counting function calls (@counter)
• Caching function results

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