Decorators

In python everything is an object. Even functions, and they can be passed as parameters.

Decorators without args, *kwargs

def outfun(somefun):
    def infun():
        print('inside infun')
        return somefun()
    return infun

def arbitraryFun():
    print('this is an arbitrary function')

func = outfun(arbitraryFun)
func()

output

inside infun

this is an arbitrary function

Note

The above and the below codes does the same job, the only different is in syntax. In the code below there is an @ symbol along with the function name. That is a decorator.

def outfun(somefun):
    def infun():
        print('inside infun')
        return somefun()
    return infun

@outfun
def arbitraryFun():
    print('this is an arbitrary function')

# func = outfun(arbitraryFun)
# func()
arbitraryFun()
'''
So basically the commented lines and the last line are equivalent. 
'''

output

inside infun

this is an arbitrary function

def call_as_variable(fun):
    return fun()

@call_as_variable
def function():
    s = 'you make me un poco loco'
    return s 

print(function)

output

'you make me un poco loco'

Decorators with arguments

def outermost(arg):
    def middle(func):
        def inner():
            func()
            print(arg)
            return  
        return inner 
    return middle

@outermost('thing')
def function():
    print('some')

function()

output

some thing

Class decorators

class deco:
    def __init__(self,func) -> None:
        self.func = func 

    def __call__(self,*a,**kw):
        return self.func(*a,**kw) + ' with other string'

@deco
def function():
    return 'some string' 

function()

output

'some string with other string'