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

[Paul Morrow]

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...


    1. Define a function to be executed at exit. Note that the function 
isn't actually "wrapped" in the usual sense.

def onexit(f):
     import atexit
     atexit.register(f)
     return f

@onexit
def func():
     ...

    2. Define a class with a singleton instance. Note that once the 
class disappears enterprising programmers would have to be more creative 
to create more instances. (From Shane Hathaway on python-dev.)

def singleton(cls):
     instances = {}
     def getinstance():
         if cls not in instances:
             instances[cls] = cls()
         return instances[cls]
     return getinstance

@singleton
class MyClass:
     ...