Python Decorator Wraps
A decorator in Python is a function that expands the functionality of another function without changing the original function. A decorator produces a new function with changed behavior after wrapping the original function.
Here's an example of a simple decorator that adds a greeting before a function is called:
def add_greeting(func):
def wrapper(*args, **kwargs):
print("Hello!")
return func(*args, **kwargs)
return wrapper
In this example, add_greeting is the decorator function. It accepts the function to be embellished, func, as an input. wrapper is the inner function that actually wraps the original function.
Using *args and **kwargs, the wrapper method accepts any amount of arguments and keyword arguments.
It displays, "Hi!" before calling the original function func with those arguments and keyword arguments using return func(*args, **kwargs).
To use the add_greeting decorator to modify the behavior of a function, you can apply the decorator to the function using the @ symbol:
@add_greeting
def say_hello():
print("Hello, world!")
This is equivalent to calling say_hello = add_greeting(say_hello).
Now, when you call say_hello(), the decorator adds the greeting "Hello!" before executing the original function:
>>> say_hello()
Hello!
Hello, world!
A decorator in Python is a unique class of function that has the ability to improve or alter the performance of another function.
The "@" sign is used to specify decorators, which are applied to the function that comes after the decorator function's name. Decorators can be used to extend the usefulness of already existing methods, alter their behavior, or offer a means of encapsulating and reusing code.
A decorator function accepts another function as input and produces a new function that adds new functionality to the input function.
The wrapping function can modify the input arguments, perform some pre-processing or post-processing steps, or handle exceptions that might be raised by the original function.
One common use case for decorators is to add logging or timing functionality to functions without modifying the original code. For instance, the code that follows specifies a straightforward decorator that records a function's inputs and return value:
def log(func):
def wrapper(*args, **kwargs):
print(f"Calling {func.__name__} with args={args}, kwargs={kwargs}")
result = func(*args, **kwargs)
print(f"{func.__name__} returned {result}")
return result
return wrapper
@log
def my_function(a, b):
return a + b
my_function(1, 2)
Output:
Calling my_function with args=(1, 2), kwargs={}
my_function returned 3
In this example, the log decorator wraps the my_function function by defining a new function called wrapper that adds logging before and after calling the original function. The @log syntax applies the log decorator to the my_function function, causing it to be wrapped with the logging behavior.
When my_function is called with the arguments (1, 2), the wrapper function defined by the log decorator is called instead, and it logs the input arguments before calling the original function.
After my_function returns a value of 3, the wrapper function logs the return value and returns it to the caller.
A decorator is a unique Python component that can be used to change a function's or a class's behavior. Decorators are essentially functions that take another function or class as input, and then modify or extend its behavior in some way.
A decorator can be used to wrap a function or a class by defining a new function that takes the original function or class as an argument, and then returns a modified version of the original. Here's an example of a simple decorator that wraps a function:
def my_decorator(func):
def wrapper():
print("Before function is called.")
func()
print("After function is called.")
return wrapper
@my_decorator
def say_hello():
print("Hello!")
say_hello()
In this instance, the function my decorator accepts the input of another function (func) and produces a brand-new function (wrapper).
The wrapper function is defined to print some messages before and after calling the original function (func), which is called in the middle.
The my decorator decorator is applied to the say hello method using the @my decorator notation. When say_hello is called, the wrapper function returned by my_decorator is actually called, and it first prints "Before function is called.", then calls the original say_hello function, which prints "Hello!", and finally prints "After function is called.".
This way, the decorator can modify the behavior of the original function without actually changing its source code. Decorators are a powerful tool in Python, and can be used for a wide variety of purposes, such as logging, authentication, caching, and more.