Function Decorator in Python

Following are important facts about functions in Python that are useful to understand decorator functions.

1.In Python, we can define a function inside another function.
2.In Python, a function can be passed as parameter to another function (a function can also return another function).

# A Python program to demonstrate that a function
# can be defined inside another function and a
# function can be passed as parameter.
# Adds a welcome message to the string
def messageWithWelcome(str):

# Nested function
def addWelcome():

return "Welcome to "

# Return concatenation of addWelcome()
# and str.
return addWelcome() + str

# To get site name to which welcome is added
def site(site_name):

return site_name

print messageWithWelcome(site("PythonWorld"))

Output:

Welcome to PythonWorld

Function Decorator

A decorator is a function that takes a function as its only parameter and returns a function. This is helpful to “wrap” functionality with the same code over and over again. For example, above code can be re-written as following.
We use @func_name to specify a decorator to be applied on another function.

# Adds a welcome message to the string
# returned by fun(). Takes fun() as
# parameter and returns welcome().
def decorate_message(fun):

# Nested function def addWelcome(site_name):

return "Welcome to " + fun(site_name)

# Decorator returns a function
return addWelcome

@decorate_message
def site(site_name):

return site_name;

# Driver code # This call is equivalent to call to # decorate_message() with function # site("GeeksforGeeks") as parameter print site("PythonWorld")

Output:

Welcome to PythonWorld