Re: [Tutor] what does the "@" operator mean?
Am 16.12.2008 02:03, Alan Gauld schrieb: "Marc Tompkins" wrote If you're just starting out in Python, decorators can be hard to get your head around... I've been using Python for oover 10 years and still find decorators hard to get my head around! :-) I confess I'm not a fan, they go against the Python spirit of explicit is best in my opinion. If I'm calling a function I like to know I'm calling a function... I know they make the code look pretty but IMHO they are a pain to debug and I'm never totally convinced I've got it exactly right. Alan G Just found this via dzone.org: http://gumuz.nl/weblog/simple-python-decorator-classes/ Very interesting read. HTH, Wolfram ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] what does the "@" operator mean?
On Tue, 16 Dec 2008 01:03:55 +, Alan Gauld wrote: > "Marc Tompkins" wrote > >> If you're just starting out in Python, decorators can be hard to get >> your head around... > > I've been using Python for oover 10 years and still find decorators hard > to get my head around! :-) > > I confess I'm not a fan, they go against the Python spirit of explicit > is best in my opinion. If I'm calling a function I like to know I'm > calling a function... I know they make the code look pretty but IMHO > they are a pain to debug and I'm never totally convinced I've got it > exactly right. I usually think about decorator as a tag or marker instead of function calling. When I put the property decorator, I'll be thinking about attaching a property tag to the function so the interpreter would handle the function as if it is a property. This way, I don't think of it as implicit function calling but as an explicit tag (how the tag system works is a detail I need not to care). ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] what does the "@" operator mean?
> From: "Alan Gauld" > Subject: Re: [Tutor] what does the "@" operator mean? Thinking it's quite funny, I'll keep on with italian words: the @ is called "chiocciola" which means snail, while # is called "cancelletto" which is a small gate As you see italian words are quite close to the sign shape, like in Denmark i guess (trunk-a for @ is fantastic! :-P ) ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] what does the "@" operator mean?
"Paul McGuire" wrote and "#" as the "Number sign", although all of us have probably been instructed by voice mail menus to press the "pound key" when they mean this sign. In the UK its usually referred to as hash or square. When tone dial phones were first introduced in the UK in the late 70's the official documentation nearly always referred to it as square, but nowadays hash seems much more common. ( I was recently on an IVR where it started out using hash but then switched to square for a few options then back to hash again. I suspect I found a route to a relic from the past :-) Alan G. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] what does the "@" operator mean?
Marc Tompkins wrote: By the way, (totally off-topic, of course, my apologies): what do all y'all call the "@" operator? Here in the States, we call it the "at-sign", which I find boring; I believe "sleepycat" is a Scandinavian thing (I picked it up in some long-forgotten article) Continuing of the OT lane I'm not sure that "sleepycat" is scandinavien, I'm Danish myself and to my knowledge in both Denmark and Sweden the at-sign is called "snabel-a" which translates to "trunk-a" (a trunk as on an elefant) And in Norwegian I belive to be "krølle-alfa" translated means "curly-alpha" ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] what does the "@" operator mean?
I use decorators only to declare class methods. Denis Le lundi 15 décembre 2008 à 18:33 -0800, Marc Tompkins a écrit : > Does anybody who reads this list use decorators and have a nice word > to say about them? I'd be interested to hear it. > ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] what does the "@" operator mean?
> By the way, (totally off-topic, of course, my apologies): what do all > y'all call the "@" operator? Back when the "what syntax should we use for decorators?" debate raged, this symbol was referred to as a "pie", I guess because it looks like the swirl on top of a cream pie. I think this term is of Perl/Unix-y origin, similar to "bang"(!), "splat"(*), and "hash"(#). I much prefer the "spidermonkey" or "sleepycat" terms, though. Unfortunately, here in the US, far fewer would understand what I was saying than if I called it the prosaic "at-sign" (so named because on old-style store receipts, one might find "3 apples @ 5 cents", meaning "at the unit price of" or just "at" for short). Use of "dot" and "star" for "." and "*" are fairly commonplace now, in place of their older forms "period" and "asterisk". Did you ever hear anyone say "go to 'www period google period com'"? But it is interesting that the clunky "ampersand" persists. Perhaps as we move forward into the unicode world, we will have to have more names for symbols like "§" and "¶". My Windows character map names these (when mousing over them) as the "section sign" and "Pilcrow sign". "@" is referred to here as the "Commercial At", and "#" as the "Number sign", although all of us have probably been instructed by voice mail menus to press the "pound key" when they mean this sign. Much more good info on all this trivia at http://en.wikipedia.org/wiki/Punctuation. -- Paul Mary love to wear her skates/Upon the ice to frisk/Wasn't she a silly girl/Her little * ? ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] what does the "@" operator mean?
On Mon, Dec 15, 2008 at 5:03 PM, Alan Gauld wrote:
>
> "Marc Tompkins" wrote
>
>> If you're just starting out in Python, decorators can be hard to get
>> your head around...
>
> I've been using Python for oover 10 years and still find decorators
> hard to get my head around! :-)
>
> I confess I'm not a fan, they go against the Python spirit of
> explicit is best in my opinion. If I'm calling a function I like to
> know I'm calling a function... I know they make the code look
> pretty but IMHO they are a pain to debug and I'm never totally
> convinced I've got it exactly right.
I thought this way for a while, but I "get" them now. Mostly I use
them as a shortcut to setting some variables on a function, which
could later be used for introspection. For instance, a dead simple
test framework I wrote uses decorators like this:
@test("Just load something",removefiles=["sprite1.txt"],teardown=sprite_cleanup)
def load_sprite():
f = open("sprite1.txt","w")
f.write("""texture metatex1.png
horizontal 2\nvertical 2\nlength 4\nloops 3""")
f.close()
The decorator signifies to the testing framework that this function should
be run, the file sprite1.txt should be removed after running the test, and
the function sprite_cleanup should be run as well. This could have been
done in other ways, but it is a lot more clear with a decorator.
"Hey testing framework, here is how you should run this function"
The actual code for the decorator is not complex either:
def test(t,removefiles=[],teardown=None):
def dec(f):
f.a_test = True
f.test_desc = t
f.removefiles = removefiles
f.teardown = teardown
return f
return dec
The function in a function is a bit headache inducing, I'll grant that. But the
dec function just sets some variables on the function. This could be done
in the old way:
def test(f,t,removefiles=[],teardown=None):
f.a_test = True
f.test_desc = t
With the functions decorated like this:
def test_sprites:
[code]
test(test_sprites,"Just load
something",removefiles=["sprite1.txt"],teardown=sprite_cleanup)
For me though, it is MUCH better to have this information before the
function instead of after.
Another place I am using them is in an interpreter class. The class
has various methods
tied to different commands that it understands. I also have a gui
where commands
can be chosen, according to the category of the command. The
decorator is used to
add some information that the gui can use about the nature of the
command, and which
category it falls under.
I don't used any advanced features of decorators at all, they just
make the code a little
bit more clear and allow me to do a bit more introspection of
functions for various purposes.
I don't use them often, but I do like them.
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Re: [Tutor] what does the "@" operator mean?
"Marc Tompkins" wrote y'all call the "@" operator? Here in the States, we call it the "at-sign", Thats what I've always heard in the UK too. Alan G. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] what does the "@" operator mean?
OK, having looked at
http://wiki.python.org/moin/PythonDecoratorLibrary again with a less
jaundiced eye, I believe my code may soon begin to contain a few of
the dreaded sleepycats...
By the way, (totally off-topic, of course, my apologies): what do all
y'all call the "@" operator? Here in the States, we call it the
"at-sign", which I find boring; I believe "sleepycat" is a
Scandinavian thing (I picked it up in some long-forgotten article);
some Russians refer to it as собака ("sobaka", dog) - again because it
looks like an animal with its tail curled up.
It occurs to me that Pythonistas should have their own name for the
thing. I propose "ourobouros" - the snake eating its own tail. Of
course, technically that's a capital O, but hey.
--
www.fsrtechnologies.com
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Re: [Tutor] what does the "@" operator mean?
The Python Wiki has some example decorators at http://wiki.python.org/moin/PythonDecoratorLibrary. I think the CGIMethod wrapper is a good intuitive example, and memoize is a good technique to add to your Python toolkit. -- Paul ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] what does the "@" operator mean?
Here is an interesting example of a decorator that munges the bytecodes of a function to optimize it: http://code.activestate.com/recipes/277940/ Kent ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] what does the "@" operator mean?
On Mon, Dec 15, 2008 at 9:33 PM, Marc Tompkins wrote: > I'm sorry I left it as flat as I did - that Dr. Dobbs article is a > pretty good explanation, and there's an article somewhere in the > Effbot bookshelf that does a decent job - but I couldn't find either > one at that moment. FWIW my attempt at explaining decorators is here: http://personalpages.tds.net/~kent37/kk/1.html > I've only been using Python for a couple of years now, but my > experience so far is the same as yours: decorators make my head hurt. > Even in the Dr. Dobbs article, the examples seem horribly contrived. It's hard to find a simple example of decorators that is not contrived. The real-world cases are often too complex for an introduction. I cite a few examples in my article. Some other examples: Django's login_required decorator: http://docs.djangoproject.com/en/dev/topics/auth/#the-login-required-decorator In the standard lib, contextlib.contextmanager makes it easy to define context managers (objects that work with the 'with' statement): http://docs.python.org/library/contextlib.html#contextlib.contextmanager and functools.wraps helps to make well-behaved decorators ;-) http://docs.python.org/library/functools.html#functools.wraps I told you it was hard to find simple examples!) Kent ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] what does the "@" operator mean?
Marc Tompkins wrote: On Mon, Dec 15, 2008 at 5:03 PM, Alan Gauld wrote: I've been using Python for oover 10 years and still find decorators hard to get my head around! :-) I've only been using Python for a couple of years now, but my experience so far is the same as yours: decorators make my head hurt. Interesting. I actually rather like them and find them to be a tool to clean up code quite a bit. Python's ability to have classes offer "attributes" which are really handled by wrapper functions is a similar animal (in the sense that they can be very nice but also could be horribly abused to make smelly code). That said, I don't find myself using them too often. Sort of like a special seasoning you add to the occasional dish but exotic enough to taste weird if you used it all the time. For example, creating web apps in TurboGears uses decorators to expose methods, apply error handling and output templates without unnecessarily cluttering all your method definitions. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] what does the "@" operator mean?
On Mon, Dec 15, 2008 at 5:03 PM, Alan Gauld wrote: > > "Marc Tompkins" wrote > >> If you're just starting out in Python, decorators can be hard to get >> your head around... > > I've been using Python for oover 10 years and still find decorators > hard to get my head around! :-) > > I confess I'm not a fan, they go against the Python spirit of > explicit is best in my opinion. If I'm calling a function I like to > know I'm calling a function... I know they make the code look > pretty but IMHO they are a pain to debug and I'm never totally > convinced I've got it exactly right. > > Alan G > > ___ > Tutor maillist - Tutor@python.org > http://mail.python.org/mailman/listinfo/tutor > I'm sorry I left it as flat as I did - that Dr. Dobbs article is a pretty good explanation, and there's an article somewhere in the Effbot bookshelf that does a decent job - but I couldn't find either one at that moment. I've only been using Python for a couple of years now, but my experience so far is the same as yours: decorators make my head hurt. Even in the Dr. Dobbs article, the examples seem horribly contrived. There must be plenty of programmers who use decorators all the time and would feel lost without them, but I have yet to see a compelling use case. (It's always something like "Here's another useless, made-up situation. We could handle it in a straightforward way, but wouldn't it be cooler if we used a decorator instead?") Actually, I'm being unnecessarily harsh: I can imagine a theoretical case, where there is some operation you wish to apply to several functions, and you don't want to write the code more than once. (Wrapping a timer around functions comes to mind.) But I've never run across a situation where a decorator actually seemed like the best way to do it, and (almost) all of the articles on the subject feel like they were written to check an action item off the editor's to-do list: this book won't be complete unless we mention decorators, so better slop something together. Does anybody who reads this list use decorators and have a nice word to say about them? I'd be interested to hear it. -- www.fsrtechnologies.com p.s. - Is anybody else as sick of the phrase "syntactic sugar" as I am? ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] what does the "@" operator mean?
Thanks Chris & Marc I certainly don't need to know about decorators at this stage of my development. Maybe I'll be able to avoid them entirely Mary Lou - Original Message - From: "Chris Calloway" To: Sent: Monday, December 15, 2008 2:22 PM Subject: Re: [Tutor] what does the "@" operator mean? On 12/15/2008 3:42 PM, Marc Tompkins wrote: > If you're just starting out in Python, decorators can be hard to get > your head around... This would be a huge help: http://www.ddj.com/web-development/184406073 -- Sincerely, Chris Calloway http://www.secoora.org office: 332 Chapman Hall phone: (919) 599-3530 mail: Campus Box #3300, UNC-CH, Chapel Hill, NC 27599 ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] what does the "@" operator mean?
"Marc Tompkins" wrote If you're just starting out in Python, decorators can be hard to get your head around... I've been using Python for oover 10 years and still find decorators hard to get my head around! :-) I confess I'm not a fan, they go against the Python spirit of explicit is best in my opinion. If I'm calling a function I like to know I'm calling a function... I know they make the code look pretty but IMHO they are a pain to debug and I'm never totally convinced I've got it exactly right. Alan G ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] what does the "@" operator mean?
On 12/15/2008 3:42 PM, Marc Tompkins wrote: > If you're just starting out in Python, decorators can be hard to get > your head around... This would be a huge help: http://www.ddj.com/web-development/184406073 -- Sincerely, Chris Calloway http://www.secoora.org office: 332 Chapman Hall phone: (919) 599-3530 mail: Campus Box #3300, UNC-CH, Chapel Hill, NC 27599 ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] what does the "@" operator mean?
On Mon, Dec 15, 2008 at 12:33 PM, Mary Lou Knack wrote: > I'm looking at some code from Enthought's ETS examples and ran across the > following statement: > > @mayavi2.standalone > > I have no idea what the "@" operator means, if anything. I tried searching > for it in the documentation (locally and online), but no luck. Or rather, > the local (windows) help said it couldn't search for that phrase (@) and the > online search turned up a bazillion hits and I don't know how to refine the > search. It indicates a decorator. Try this: http://en.wikipedia.org/wiki/Python_syntax_and_semantics#Decorators If you're just starting out in Python, decorators can be hard to get your head around... -- www.fsrtechnologies.com ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] what does the "@" operator mean?
I'm looking at some code from Enthought's ETS examples and ran across the following statement: @mayavi2.standalone I have no idea what the "@" operator means, if anything. I tried searching for it in the documentation (locally and online), but no luck. Or rather, the local (windows) help said it couldn't search for that phrase (@) and the online search turned up a bazillion hits and I don't know how to refine the search. Knowledge isn't necessary for me to proceed, but it sure would be nice. Thanks. Mary Lou Knack___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
