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decorators - mp3909 - Mar-19-2018

How do I pass an argument z to my decorator function? Here is my code:

def partial(func,z):
  def wrapper(first, second):
    first = first*z
    return func(first, second)
  return wrapper
  
@partial()     #I need to pass z here, how do I do this here?
def add(first, second):
  return first+second


RE: decorators - Larz60+ - Mar-19-2018

see: http://scottlobdell.me/2015/04/decorators-arguments-python/

RE: decorators - mp3909 - Mar-19-2018

I looked on here, but it doesn't really help as my situation is different - my decorator takes 2 arguments, one of course is the function I want to decorate and the other is just a variable z.
The examples in the post you shown suggest adding another layer to my decorator function which doesn't achieve what I want.

def partial(func,z):
  def wrapper(first, second):
    first = first*z
    return func(first, second)
  return wrapper
return partial
   
@real_decorator(4)
def add(first, second):
  return first+second
I guess what I am trying to ask is how do I write this

add = partial(add,4)
as:

@partial
def add(first, second)
  return first+second
where do I put the 4?

RE: decorators - micseydel - Mar-19-2018

Hopefully this helps
def perma_set_first_param_decorator(x):
    """
    Decorates a two-argument function, replacing the first argument
    with the provided x value here.
    """
    def wrapper(f):
        return lambda y: f(x, y)

    return wrapper

@perma_set_first_param_decorator(2)
def add(first, second):
    return first + second

print(add(5)) # prints 7


RE: decorators - mp3909 - Mar-19-2018

Sorry, I am not sure if people understand my problem.
Let me explain it again.
I have a function called add which takes two arguments and return the addition of them arguments.
Here is my add function:

def add(first, second):
  return first+second
I now want to decorate this function so that the first argument is always multiplied by 4 and then added to the second argument.
So if add(2,5) then it will return 2*(4)+5 = 13, if add(3,6) then it will return 3*(4)+6 = 18.

RE: decorators - micseydel - Mar-19-2018

(Mar-19-2018, 05:31 PM)mp3909 Wrote: I now want to decorate this function so that the first argument is always multiplied by 4 and then added to the second argument.
From the way you describe it, your decorator will not care what the function it's decorating does. Am I correct in saying what you actually want is a decorator which multiplies the first argument by a value provided to the decorator, before calling the decorated function?

I believe that in either case, my example should be fairly adaptable. Feel free to give it a try, and we can work from there.

RE: decorators - mp3909 - Mar-19-2018

(Mar-19-2018, 05:48 PM)micseydel Wrote: From the way you describe it, your decorator will not care what the function it's decorating does. Am I correct in saying what you actually want is a decorator which multiplies the first argument by a value provided to the decorator, before calling the decorated function
- YES!

I have got this far in terms of trying to achieve it:

def primer(func, z):
  def wrapper(*args,**kwargs):
    # I need to multiply the first argument by z so something like arg=arg*z before I pass this argument into the function in next line
    return func(*args, **kwargs)
  return wrapper
  
@primer
def add(first, second):
  return first+second


RE: decorators - wavic - Mar-19-2018 

In [1]: def decorator(func):
   ...:     def wrapper(first, second):
   ...:         first *= 4
   ...:         return func(first, second)
   ...:     return wrapper
   ...: 

In [2]: @decorator
   ...: def add(first, second):
   ...:     return first + second
   ...: 

In [3]: result = add(1, 4)

In [4]: print(result)
8


RE: decorators - mp3909 - Mar-19-2018

Thank You Wavic!!
Much appreciated.

RE: decorators - mp3909 - Mar-25-2018

I am trying to build decorators within decorators.
I thought I take the example I have discussed previously.
I have a function that multiplies x and y.
My decorator function just prints out a statement saying "x*y = "
I have now added a superdecorator function around my decorator function where I now want to multiply (n*x)*(n*y) i.e. if n=2 then I want to multiply the double of x and the double of y.
Here is my code below but I am getting an error message saying :

print('{} * {} = '.format(*args*n,**kwargs*n), end='')
TypeError: unsupported operand type(s) for *: 'dict' and 'int'
def superdecorator(n):
    def decorator(func):
        def wrapped(*args, **kwargs):
            print('{} * {} = '.format(*args*n,**kwargs*n), end='')
            return func(*args*n, **kwargs*n)
        return wrapped
    return decorator


@superdecorator(2)
def mult(x,y):
    return x*y