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Decorators with parameters in Python

Prerequisite : Decorators in Python

Python functions are First Class citizens which means that functions can be treated similar to objects.

  • Function can be assigned to a variable i.e they can be referenced.
  • Function can be passed as an argument to another function.
  • Function can be returned from a function.

Decorators with parameters is similar to normal decorators.

Syntax for decorators with parameters

@decorator(params)
def func_name():
    ''' Function implementation'''

The above code is equivalent to



def func_name():
    ''' Function implementation'''

func_name = (decorator(params))(func_name)
"""

As the execution starts from left to right decorator(params) is called which returns a function object fun_obj. Using the fun_obj the call fun_obj(fun_name) is made. Inside the inner function, required operations are performed and the actual function reference is returned which will be assigned to func_name. Now, func_name() can be used to call the function with decorator applied on it.

Above code can be visualized step by step here

How Decorator with parameters is implemented

   
def decorators(*args, **kwargs):
    def inner(func):
        '''
           do operations with func
        '''
        return func
    return inner #this is the fun_obj mentioned in the above content
  
@decorators(params)
def func():
    """
         function implementation
    """

Here params can also be empty.
Above code can be visualized step by step here

Example

# Python code to illustrate
# Decorators with parameters in Python
  
def decorator(*args, **kwargs):
    print("Inside decorator")
    def inner(func):
        print("Inside inner function")
        print("I like", kwargs['like']) 
        return func
    return inner
  
@decorator(like = "geeksforgeeks")
def func():
    print("Inside actual function")
  
func()

Output

Inside decorator
Inside inner function
I like geeksforgeeks
Inside actual function

This example also tells us that Outer function parameters can be accessed by the enclosed inner function.

1. Inside the Decorator

2. Inside the function

The above example can be visualized step by step here.
Note : Image snapshots are taken using PythonTutor



This article is attributed to GeeksforGeeks.org

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