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Date: Sun, 26 Apr 2015 21:24:26 -0700
From: Ethan Furman <ethan@stoneleaf.us>
To: python-list@python.org
Subject: Re: Function decorator having arguments is complicated
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On 04/27, Makoto Kuwata wrote:
> 
> I feel that function decorator having arguments is complicated,
> because three 'def' are nested:
> 
>   def multiply(n):
>     def deco(func):
>       def newfunc(*args, **kwargs):
>         return n * func(*args, **kwargs)
>       return newfunc
>     return deco

When I have to write an argument-taking decorator, I use a class:

    class multiply(object):  # don't need 'object in 3.x'

        def __init__(self, n):
            self.n = n

        def __call__(self, func):
            def newfunc(*args, **kwargs):
                return self.n * func(*args, **kwargs)
            return newfunc

>   @multiply(4)
>   def f1(x, y):
>     return x+y
> 
>   print(f1(2, 3))   #=> 20  (= 4 * (2+3))

This all works the same.
> 
> 
> If function decorator notation could take arguments,
> decorator definition would be more simple:
> 
>   def multiply(func, n):
>     def newfunc(*args, **kwargs):
>       return n * func(*args, **kwargs)
>     return newfunc
> 
>   @multiply 4      # ex: @decorator arg1, arg2, arg3
>   def f1(x, y):
>     return x+y
> 
> 
> How do you think about this idea?

It's unnecessary, just use a class instead of a function to get more
clarity.

--
~Ethan~