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Re: I love the decorator in Python!!!

References <29996186.628.1323328726122.JavaMail.geo-discussion-forums@prfb7> <jbpu9j$1af$1@r03.glglgl.gl> <jbq6li$p9o$1@dough.gmane.org>
Date 2011-12-08 22:43 +1100
Subject Re: I love the decorator in Python!!!
From Chris Angelico <rosuav@gmail.com>
Newsgroups comp.lang.python
Message-ID <mailman.3408.1323344595.27778.python-list@python.org> (permalink)

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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

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Thread

I love the decorator in Python!!! 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-07 23:18 -0800
  Re: I love the decorator in Python!!! Chris Rebert <clp2@rebertia.com> - 2011-12-08 00:04 -0800
  Re: I love the decorator in Python!!! Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2011-12-08 09:59 +0100
    Re: I love the decorator in Python!!! Chris Angelico <rosuav@gmail.com> - 2011-12-08 20:37 +1100
    Re: I love the decorator in Python!!! K.-Michael Aye <kmichael.aye@gmail.com> - 2011-12-08 12:22 +0100
      Re: I love the decorator in Python!!! Francesco Bochicchio <bieffe62@gmail.com> - 2011-12-09 04:00 -0800
    Re: I love the decorator in Python!!! Chris Angelico <rosuav@gmail.com> - 2011-12-08 22:43 +1100
      Re: I love the decorator in Python!!! Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2011-12-09 10:57 +0100
      Re: I love the decorator in Python!!! 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-09 10:28 -0800
        Re: I love the decorator in Python!!! 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-09 16:21 -0800
        Re: I love the decorator in Python!!! 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-09 16:21 -0800
          Re: I love the decorator in Python!!! 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-10 06:04 -0800
            Re: I love the decorator in Python!!! 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-10 06:09 -0800
              Re: I love the decorator in Python!!! alex23 <wuwei23@gmail.com> - 2011-12-11 19:35 -0800
            Re: I love the decorator in Python!!! 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-10 06:09 -0800
          Re: I love the decorator in Python!!! 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-10 06:04 -0800
      Re: I love the decorator in Python!!! 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-09 10:28 -0800
    Re: I love the decorator in Python!!! K.-Michael Aye <kmichael.aye@gmail.com> - 2011-12-08 17:24 +0100
    Re: I love the decorator in Python!!! Chris Angelico <rosuav@gmail.com> - 2011-12-09 03:38 +1100
      Re: I love the decorator in Python!!! alex23 <wuwei23@gmail.com> - 2011-12-08 21:02 -0800
        Re: I love the decorator in Python!!! Robert Kern <robert.kern@gmail.com> - 2011-12-09 10:08 +0000
          Re: I love the decorator in Python!!! alex23 <wuwei23@gmail.com> - 2011-12-11 19:36 -0800
            Re: I love the decorator in Python!!! 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-11 20:51 -0800
              Re: I love the decorator in Python!!! alex23 <wuwei23@gmail.com> - 2011-12-11 21:47 -0800
                Re: I love the decorator in Python!!! 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-12 04:16 -0800
            Re: I love the decorator in Python!!! Ethan Furman <ethan@stoneleaf.us> - 2011-12-11 23:47 -0800
            Re: I love the decorator in Python!!! Robert Kern <robert.kern@gmail.com> - 2011-12-12 16:27 +0000
              Re: I love the decorator in Python!!! alex23 <wuwei23@gmail.com> - 2011-12-12 16:46 -0800
    Re: I love the decorator in Python!!! Andrew Berg <bahamutzero8825@gmail.com> - 2011-12-08 10:54 -0600
    Re: I love the decorator in Python!!! Andrew Berg <bahamutzero8825@gmail.com> - 2011-12-08 10:55 -0600
    Re: I love the decorator in Python!!! Ethan Furman <ethan@stoneleaf.us> - 2011-12-08 15:34 -0800
    Re: I love the decorator in Python!!! Ethan Furman <ethan@stoneleaf.us> - 2011-12-08 15:56 -0800

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