We know Decorators are a very powerful and useful tool in Python since it allows programmers to modify the behavior of function or class. In this article, we will learn about the Decorators with Parameters with help of multiple examples.
Python functions are First Class citizens which means that functions can be treated similarly 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.
The 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.
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.
Observe these first :
# Python code to illustrate
# Decorators basic in Python
def decorator_fun(func):
print("Inside decorator")
def inner(*args, **kwargs):
print("Inside inner function")
print("Decorated the function")
# do operations with func
func()
return inner
@decorator_fun
def func_to():
print("Inside actual function")
func_to()
Another Way:
# Python code to illustrate
# Decorators with parameters in Python
def decorator_fun(func):
print("Inside decorator")
def inner(*args, **kwargs):
print("Inside inner function")
print("Decorated the function")
func()
return inner
def func_to():
print("Inside actual function")
# another way of using decorators
decorator_fun(func_to)()
Output:
Inside decorator
Inside inner function
Decorated the function
Inside actual function
Let’s move to another example:
Example #1:
# Python code to illustrate
# Decorators with parameters in Python
def decorator(*args, **kwargs):
print("Inside decorator")
def inner(func):
# code functionality here
print("Inside inner function")
print("I like", kwargs['like'])
func()
# reurning inner function
return inner
@decorator(like = "prutor")
def my_func():
print("Inside actual function")
Output:
Inside decorator
Inside inner function
I like prutor
Inside actual function
Example #2:
# Python code to illustrate
# Decorators with parameters in Python
def decorator_func(x, y):
def Inner(func):
def wrapper(*args, **kwargs):
print("I like prutor.ai")
print("Summation of values - {}".format(x+y) )
func(*args, **kwargs)
return wrapper
return Inner
# Not using decorator
def my_fun(*args):
for ele in args:
print(ele)
# another way of using dacorators
decorator_func(12, 15)(my_fun)('prutor', 'dot', 'ai')
Output:
I like prutor.ai
Summation of values - 27
prutor
dot
ai
This example also tells us that Outer function parameters can be accessed by the enclosed inner function.
Example #3:
# Python code to illustrate
# Decorators with parameters in Python (Multi-level Decorators)
def decodecorator(dataType, message1, message2):
def decorator(fun):
print(message1)
def wrapper(*args, **kwargs):
print(message2)
if all([type(arg) == dataType for arg in args]):
return fun(*args, **kwargs)
return "Invalid Input"
return wrapper
return decorator
@decodecorator(str, "Decorator for 'stringJoin'", "stringJoin started ...")
def stringJoin(*args):
st = ''
for i in args:
st += i
return st
@decodecorator(int, "Decorator for 'summation'n", "summation started ...")
def summation(*args):
summ = 0
for arg in args:
summ += arg
return summ
print(stringJoin("I ", 'like ', "prutor", 'for', "prutor"))
print()
print(summation(19, 2, 8, 533, 67, 981, 119))
Output:
Decorator for 'stringJoin'
Decorator for 'summation'
stringJoin started ...
I like prutor.ai
summation started ...
1729
1. Inside the Decorator
2. Inside the function
Note: Image snapshots are taken using PythonTutor.