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pythonpython-decorators
Tania
Tania

Reputation: 1925

Python decorators. Error while passing arguments

I am trying to wrap my head around decorators. So I tried passing arguments to a decorator and processing them inside the decorator function. I just pass a list to the decorator and want my list to be processed inside the decorator function after calling the original function. Here's my code

def decorator_function(original_function):
    def new_function(*args, **kwargs):
        print("Your list shall be processed now.")
        print args
        #Do something with the passed list here.Say, call a function Process(list,string)
        original_function(*args, **kwargs) 
    return new_function



@decorator_function([1,2,3])
def hello(name = None):
    if name == None:
        print "You are nameless?"
    else:
        print "hello there,",name

hello("Mellow")

I get this error

Your list shall be processed now.
(<function hello at 0x7f9164655758>,)
Traceback (most recent call last):
  File "anno_game.py", line 14, in <module>
    def hello(name = None):
  File "anno_game.py", line 8, in new_function
    original_function(*args, **kwargs) 
TypeError: 'list' object is not callable

Can anyone please tell me what have I messed up here and point me in the right direction?

Upvotes: 0

Views: 290

Answers (1)

warvariuc
warvariuc

Reputation: 59604

def decorator_function(original_function):
    def new_function(*args, **kwargs):
        print("Your list shall be processed now.")
        print args
        #Do something with the passed list here.Say, call a function Process(list,string)
        original_function(*args, **kwargs) 
    return new_function

@decorator_function([1,2,3])
def hello(name = None):
    if name == None:
        print "You are nameless?"
    else:
        print "hello there,",name

hello("Mellow")

When you do @decorator_function([1,2,3]) decorator_function is called with [1,2,3] passed to it as original_function argument, which you are trying to call original_function(*args, **kwargs).

To have the decorator to receive a list, you need to make another wrapper:

def decorator_function(a_list):

        print("Your list shall be processed now.", a_list)
        #Do something with the passed list here.Say, call a function Process(a_list)

    def wrapper(original_function):

        def new_function(*args, **kwargs):

            print("Your list with function args shall be processed now.", a_list, args)
            #Do something with the passed list here.  Say, call a function Process(a_list, args)

            original_function(*args, **kwargs) 

        return new_function

    return wrapper

Upvotes: 1

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