Python decorators are a powerful feature that allows programmers to modify the behavior of functions or classes in a program. They are commonly used to add functionality to existing code without having to modify the original code. Decorators in Python can take inputs, which can make them even more flexible. In this guide, we will explain how to use Python decorators and allow for them to have inputs.

Step 1: Defining a Decorator

To define a decorator, we first need to create a function that will take another function as an argument. The decorator function will modify the behavior of the input function, so it needs to have access to the input function's code. Here is an example of a decorator function:

def my_decorator(func):
    def wrapper():
        print("Before the function is called.")
        func()
        print("After the function is called.")
    return wrapper

In this example, the my_decorator() function takes another function as an argument (func). It then defines a new function (wrapper()) that modifies the behavior of the input function. The wrapper() function includes code that will be executed before and after the input function is called.

Step 2: Applying the Decorator

Now that we have defined a decorator function, we can apply it to an existing function. To do this, we simply need to add the decorator function's name (without parentheses) above the function we want to modify. For example:

@my_decorator
def say_hello():
    print("Hello!")

In this example, we are applying the my_decorator() function to the say_hello() function. When we call say_hello(), the my_decorator() function will modify its behavior by adding the code defined in the wrapper() function.

Step 3: Adding Inputs to the Decorator

To allow our decorator to take inputs, we need to modify the decorator function to accept arguments. We can do this by adding arguments to the decorator function's definition. For example:

def my_decorator_with_input(input_arg):
    def real_decorator(func):
        def wrapper():
            print("Before the function is called. Input argument is:", input_arg)
            func()
            print("After the function is called. Input argument is:", input_arg)
        return wrapper
    return real_decorator

In this modified example, the my_decorator_with_input() function now takes an input_arg argument. This function returns another function (real_decorator()) which in turn returns the wrapper() function. The real_decorator() function takes the input function as an argument (func), and the wrapper() function modifies its behavior by adding the input_arg argument.

Step 4: Applying the Decorator with Inputs

To apply the decorator with inputs, we simply need to pass the arguments to the decorator function when we apply it to our input function. For example:

@my_decorator_with_input("world")
def say_hello():
    print("Hello!")

In this example, we are applying the my_decorator_with_input() function to the say_hello() function with an input_arg of "world". When we call say_hello(), the my_decorator_with_input() function will modify its behavior by adding the input_arg argument to the wrapper() function.

Conclusion

In this guide, we have explained how to use Python decorators and allow for them to have inputs. By following these steps, you can create powerful decorators that can modify the behavior of functions or classes in your program.