[Python-Dev] Re: __metaclass__ and __author__ are already decorators

[Paul Morrow]

Bob Ippolito wrote:

> 
> On Aug 21, 2004, at 6:54 PM, Paul Morrow wrote:
> 
>> Bob Ippolito wrote:
>>
>>> On Aug 21, 2004, at 6:24 PM, Paul Morrow wrote:
>>>
>>>>
>>>> It seems that writing a decorator is going to be a bizarre 
>>>> experience. In the example, I would need to write a function named 
>>>> 'decoration' that returns a function that will recieve a function 
>>>> (foo) to be decorated and then return a function.  Does that sound 
>>>> about right?
>>>
>>> Yes that is correct.
>>>
>>>> What would functions like 'decoration' typically look like?  Could 
>>>> you show a short code snippet?
>>>
>>> http://python.org/peps/pep-0318.html
>>
>>
>> Thanks.  Of the 5 examples there, the first two are apparently not 
>> implemented correctly, as they expect that the function/class to be 
>> decorated is passed directly to them, rather than to the function they 
>> return.  Would you agree?  I pasted them here for your consideration...
> 
> 
> No, they are correct.  You are confused.  What is expected is that the 
> result of the expression after @ is callable and takes one parameter.  
> If the expression after @ is just a name, then nothing particularly 
> exciting happens at that time.
> 
> @bar # NOTE THE LACK OF PARENTHESES
> def foo():
>     ....
> 
> is equivalent to:
> 
> _tmp = bar
> def foo():
>     ....
> foo = _tmp(foo)
> 
> _tmp = bar clearly doesn't do anything special
> 
> However, you're confusing that with examples that look more like:
> 
> @bar()  # NOTE THE PARENTHESES
> def foo():
>     ....
> 
> which are equivalent to:
> 
> _tmp = bar()
> def foo():
>     ....
> foo = _tmp(foo)
> 
> -bob

Yes, I was missing that.  Thanks for the detailed explanation.