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Date: Thu, 8 Dec 2011 22:43:12 +1100
Subject: Re: I love the decorator in Python!!!
From: Chris Angelico <rosuav@gmail.com>
To: python-list@python.org
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On Thu, Dec 8, 2011 at 10:22 PM, K.-Michael Aye <kmichael.aye@gmail.com> wrote:
> I am still perplexed about decorators though, am happily using Python for
> many years without them, but maybe i am missing something?
> For example in the above case, if I want the names attached to each other
> with a comma, why wouldn't I just create a function doing exactly this? Why
> would I first write a single name generator and then decorate it so that I
> never can get single names anymore (this is the case, isn't it? Once
> decorated, I can not get the original behaviour of the function anymore.

The example given is a toy. It's hardly useful. However, there are a
number of handy uses for decorators; mostly, they consist of giving a
single simple keyword to a complicated set of logic. One example is
the @classmethod and @staticmethod decorators - the code to implement
them could be uglier than nested inline assembly, but you don't have
to care, because you just type "@staticmethod" in front of your def
statement and it does its magic.

Here's a handy trick that I'm sure someone has done in a more sophisticated way:

def trace(func):
    if debugmode:
        return lambda *a,**ka:
(print(">"+func.__name__),func(*a,**ka),print("<"+func.__name__))[1]
    return func

Then you put @trace in front of all your functions, and if debugmode
is False, nothing will be done - but set it to true, and you get
console output at the entry and exit of each function.

>>> @trace
def test(x):
	print("Test! "+x)
	return 5

>>> test("asdf")
>test
Test! asdf
<test
5

Again, it's helpful because it condenses all the logic (including the
'debugmode' flag) down to a single high level directive: "Trace this
function".

ChrisA