[Python-ideas] Decorator syntax restriction
Rob Cliffe
Daniel Fetchinson
> expression? Guido has said he has a 'gut feeling' against this but has not
> as far as I know rationalised it.
>
> 1) It is inconsistent with Python in general (unPythonic) to impose
> arbitrary restrictions in one particular place, and hard to explain to
> someone learning the language.
>
> 2) The restriction is in any case more apparent than real,
> as
> @ <any-expression> # disallowed, SyntaxError
> can be implemented, albeit in a more verbose aka less Pythonic was, as:
What makes you think that if something is 'more verbose' it is 'less
pythonic'? I actually like the fact that python doesn't try condensing
everything into one-liners and special symbols.
I never really understood this need for being not verbose, but it does
periodically come up on this list (and pretty much on every other
programming list). Your fingers get tired? It takes too long to read
an extra line? You are running out of space on your harddrive? It
takes too long to transfer the source file over the network because of
the extra line?
Honestly, why do some people set for themselves the goal of "let's
have as few characters in a source file as possible"?
Cheers,
Daniel
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Mike Meyer
Daniel Fetchinson <fetch...@googlemail.com> wrote:
> What makes you think that if something is 'more verbose' it is 'less
> pythonic'? I actually like the fact that python doesn't try condensing
> everything into one-liners and special symbols.
Agreed. Readability, not succinctness, is what's pythonic. Being
succinct usually - but not always - improves readability.
> I never really understood this need for being not verbose, but it does
> periodically come up on this list (and pretty much on every other
> programming list). Your fingers get tired? It takes too long to read
> an extra line? You are running out of space on your harddrive? It
> takes too long to transfer the source file over the network because of
> the extra line?
>
> Honestly, why do some people set for themselves the goal of "let's
> have as few characters in a source file as possible"?
Paul Graham (generally a very sharp guy) summarizes most of the
reasons in http://www.paulgraham.com/power.html. I provide my attempt
at a counterargument in
http://www.mired.org/home/mwm/papers/readability.html.
<mike
--
Mike Meyer <m...@mired.org> http://www.mired.org/consulting.html
Independent Network/Unix/Perforce consultant, email for more information.
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Brett Cannon
> Can I make another plea for the syntax following '@' to be an unrestricted
> expression? Guido has said he has a 'gut feeling' against this but has not
> as far as I know rationalised it.
>
When it comes to Guido's gut, a rationalization isn't needed. Perk of
being BDFL. Plus his gut is right so often it tends to not be
questioned.
> 1) It is inconsistent with Python in general (unPythonic) to impose
> arbitrary restrictions in one particular place, and hard to explain to
> someone learning the language.
>
It's not difficult to explain; decorators can only be a dotted name w/
an optional method call and its corresponding arguments. It keeps the
syntax simple and clean, IMO. Decorators add a mental overhead of
having to think about what they will do to a function when reading the
code. If I then also have to figure out what an arbitrary expression
evaluates to in order to figure that out that is more mental effort
than needed. Yes, you can do whatever with the decorator you are
passing in, but hopefully you are not so evil/stupid as to make a
decorator that copmlicated. Give people the power of full expressions
and that will happen more often.
> 2) The restriction is in any case more apparent than real,
> as
> @ <any-expression> # disallowed, SyntaxError
> can be implemented, albeit in a more verbose aka less Pythonic was, as:
>
> AnyExpr = <any-expression>
> @AnyExpr
>
> or as
>
> def Identity(x): return x
> ...
> @Identity( <any-expression> ) # smuggle in as func arg
>
And we almost ditched lambdas in Python 3 because you can implement
them in the same way. The only reason they got to stick around was
they were already in use and people threw a fit over them.
> 3) I propose the following as plausible use cases (I know other people will
> have their own):
>
> 3.1)
> @DecoratorList[index]
>
> 3.2)
> @DecoratorDictionary[key]
>
> 3.3)
> @Decorator1 if <condition> else Decorator2
> # Special case of the last one:
> def Identity(x): return x
> @Decorator if __debug__ else Identity
>
Plausible does not equal useful. You need to show that this actually
comes up in normal coding for a decent amount of Python code to
warrant tweaking the language over.
> Xavier Morel has pointed out that 3.1) can be implemented now as
> @DecoratorList.__getitem__[index]
> but this doesn't seem a good reason for forbidding the simpler syntax; after
> all Python allows the simpler syntax in other contexts. Similarly 3.2) can
> be written as
> @DecoratorDictionary.get(key)
>
> (As an aside, perhaps a decorator that evaluates to None could be treated at
> run-time the same as no decorator, i.e. equivalent to the Identity function
> in the above examples. Currently it naturally raises TypeError: 'NoneType'
> object is not callable. Just a thought.)
That's not going to happen. =) Complicates the bytecode unnecessarily.
Once again, this needs to actually come up in regular usage to warrant
even considering the change.
>
> Finally, sorry if I have not sent this e-mail to the right place (I wanted
> to attach it to the 'allow lambdas as decorators' thread but don't yet know
> how to do this). Also sorry that this partly duplicates a message I sent to
> python-dev. I am still finding my way round the Python mailing lists.
No, this is the place to send thought out proposals for changing
Python before they get promoted to hitting python-dev.
-Brett
Nick Coghlan
> On Sun, Sep 6, 2009 at 09:41, Rob Cliffe<rob.c...@btinternet.com> wrote:
>> Can I make another plea for the syntax following '@' to be an unrestricted
>> expression? Guido has said he has a 'gut feeling' against this but has not
>> as far as I know rationalised it.
>>
>
> When it comes to Guido's gut, a rationalization isn't needed. Perk of
> being BDFL. Plus his gut is right so often it tends to not be
> questioned.
>
>> 1) It is inconsistent with Python in general (unPythonic) to impose
>> arbitrary restrictions in one particular place, and hard to explain to
>> someone learning the language.
>>
>
> It's not difficult to explain; decorators can only be a dotted name w/
> an optional method call and its corresponding arguments.
>From the last discussion, I believe Guido was actually amenable to the
idea of extending this to allow a subscript operation as well, so a
decorator could be pulled from a sequence or map of decorators without
requiring an otherwise unnecessary function call.
So what's needed at this point is for someone that is bothered by the
restriction to come up with a patch to loosen the restriction without
getting rid of it entirely.
Cheers,
Nick.
--
Nick Coghlan | ncog...@gmail.com | Brisbane, Australia
---------------------------------------------------------------
Daniel Fetchinson
>> pythonic'? I actually like the fact that python doesn't try condensing
>> everything into one-liners and special symbols.
>
> Agreed. Readability, not succinctness, is what's pythonic. Being
> succinct usually - but not always - improves readability.
>
>> I never really understood this need for being not verbose, but it does
>> periodically come up on this list (and pretty much on every other
>> programming list). Your fingers get tired? It takes too long to read
>> an extra line? You are running out of space on your harddrive? It
>> takes too long to transfer the source file over the network because of
>> the extra line?
>>
>> Honestly, why do some people set for themselves the goal of "let's
>> have as few characters in a source file as possible"?
>
> Paul Graham (generally a very sharp guy) summarizes most of the
> reasons in http://www.paulgraham.com/power.html.
Thanks, this answers my question why people think this way. Although
I'm still totally convinced that guys like Paul Graham, or anybody
else who believes in shorter code, are misguided.
> I provide my attempt at a counterargument in
> http://www.mired.org/home/mwm/papers/readability.html.
Yep, I more-or-less agree with you.
Cheers,
Daniel
--
Psss, psss, put it down! - http://www.cafepress.com/putitdown
Stephen J. Turnbull
> >> What makes you think that if something is 'more verbose' it is 'less
> >> pythonic'? I actually like the fact that python doesn't try condensing
> >> everything into one-liners and special symbols.
Yes.
> > Agreed. Readability, not succinctness, is what's pythonic. Being
> > succinct usually - but not always - improves readability.
Yes.
> >> I never really understood this need for being not verbose, but it does
> >> periodically come up on this list (and pretty much on every other
> >> programming list).
> >> Your fingers get tired?
Yes. See Jan Kaliszewski's post in the "possible attribute-oriented
class" thread. His reasoning is valid, though I don't sympathize with
it personally.
> >> It takes too long to read an extra line?
Yes, when "too long" has the semantics "I read this repeatedly in a
short space and don't need to see the whole thing over and over
again. In fact, it gets in my way when reading an 'array' of the sme
idiom."
This is what Paul Graham means by (expressive) power, I believe. He
mentions metrics like number of characters or lines, but he says what
he really wants is something like the number of leaves in the AST.
If the "this" is something local, then you use a function (or
sometimes a macro if available) at that level of locality. But if the
idiom appears across many programs, then it may be a good idea to turn
it into a standard builtin, or even syntax. I believe this is the
gist of Graham's argument, and it's very close to the criteria for
adding syntax in the Zen (actually, the apocrypha, stuff like "not
every three-line function needs to be a builtin" aren't canonized).
> >> You are running out of space on your harddrive?
> >> It takes too long to transfer the source file over the network
> >> because of the extra line?
Both of those are silly. If you use compression, it will work out
about the same anyway.<wink>
> >> Honestly, why do some people set for themselves the goal of "let's
> >> have as few characters in a source file as possible"?
Mostly the ones who show up on Python lists don't have such a goal.
They just want the ache in their hands and arms to go away, one
unnecessary character at a time.
> > Paul Graham (generally a very sharp guy) summarizes most of the
> > reasons in http://www.paulgraham.com/power.html.
>
> Thanks, this answers my question why people think this way. Although
> I'm still totally convinced that guys like Paul Graham, or anybody
> else who believes in shorter code, are misguided.
>
> > I provide my attempt at a counterargument in
> > http://www.mired.org/home/mwm/papers/readability.html.
>
> Yep, I more-or-less agree with you.
But Paul Graham does, too, AFAICS.
ISTM that what Paul G. doesn't get is that Paul P.'s epigram is more
along the lines of Emerson's epigram. To put it in the same style, "A
bogus succinctness is the hobgoblin of L2-cache-deprived minds (and
RSI-hobbled wrists)." To me, the argument on "mired" seems quite
complementary to the argument Graham makes, in that it shows how
Python actually is succinct in the sense that Graham proposes, despite
not minimizing character, token, or line counts.
Daniel Fetchinson
> gave are harder to understand, because they introduce an extra step that is
> not relevant to the job to be done; rather, it is a distraction that adds an
> extra 'kink' in the flow of thought.
I actually agree with you, in the case of decorators, and for some of
the cases you discussed (for example allowing @decorator[5] syntax),
it is true that the short forms are readable and I don't see any
problem with them.
My only concern was the general statement 'more verbose = unpythonic'.
> You may disagree - fine - but it should be up to the judgement of the
> programmer, within reason, how concise or how verbose to be.
I don't fully agree. Some obfuscated, hard-to-read, etc forms should I
think be explicitly forbidden. Luckily, python does forbid lots of
constructs which would be very hard to follow.
> In this case,
> the language should not force me to go the extra mile with an arbitrary
> restriction, when there is no reason to (no difficulty of implementation, as
> I understand it).
Yes, again, I fully agree with you on this particular case.
Cheers,
Daniel
Mike Meyer
Except we're looking at what makes an idea "good" in python terms,
vs. what makes them "not good". Basically, trying to define
"pythonic". I don't know that that can be done, but there seem to be
some broad points that can be agreed on....
> > >> Honestly, why do some people set for themselves the goal of "let's
> > >> have as few characters in a source file as possible"?
> Mostly the ones who show up on Python lists don't have such a goal.
> They just want the ache in their hands and arms to go away, one
> unnecessary character at a time.
>
> > > Paul Graham (generally a very sharp guy) summarizes most of the
> > > reasons in http://www.paulgraham.com/power.html.
> >
> > Thanks, this answers my question why people think this way. Although
> > I'm still totally convinced that guys like Paul Graham, or anybody
> > else who believes in shorter code, are misguided.
> >
> > > I provide my attempt at a counterargument in
> > > http://www.mired.org/home/mwm/papers/readability.html.
I think my choice of "counterargument" here is a bit off. It's not all
that argumentative.
> > Yep, I more-or-less agree with you.
> But Paul Graham does, too, AFAICS.
>
> ISTM that what Paul G. doesn't get is that Paul P.'s epigram is more
> along the lines of Emerson's epigram. To put it in the same style, "A
> bogus succinctness is the hobgoblin of L2-cache-deprived minds (and
> RSI-hobbled wrists)." To me, the argument on "mired" seems quite
> complementary to the argument Graham makes, in that it shows how
> Python actually is succinct in the sense that Graham proposes, despite
> not minimizing character, token, or line counts.
What I was attempting to do was point out that succinctness for the
sake of succinctness isn't necessarily a good thing. Python indeed
tries to be succinct, but balances that against the need for the
results to still be readable. I'd say that the mired.org document
supplements what Paul G. had to say rather than complements it, as the
mired.org document discusses areas where readability matters, which
Paul G. ignored.
<mike
--
Mike Meyer <m...@mired.org> http://www.mired.org/consulting.html
Independent Network/Unix/Perforce consultant, email for more information.
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Scott David Daniels
...
> What I was attempting to do was point out that succinctness for the
> sake of succinctness isn't necessarily a good thing. Python indeed
> tries to be succinct, but balances that against the need for the
> results to still be readable.
I'm quite interested in this as well. I think that a Pythonic
succinctness is very DRY (don't repeat yourself), rather than
short. What I want when I read code is to be reading ideas, not
typing or pasting. In Python, when I find I'm doing something
several times I look for ways to combine tables and code, so what
varies shows up clearly, and what is in common shows in the loop.
APL was one language that battered me over the head with the
proof that shorter was not necessarily clearer.
--Scott David Daniels
Scott....@Acm.Org
Carl Johnson
> APL was one language that battered me over the head with the
> proof that shorter was not necessarily clearer.
Ah yes, more proof of the adage: "if you can't be a good example, be a
terrible warning." :-D
— Carl Johnson
Steven D'Aprano
> APL was one language that battered me over the head with the
> proof that shorter was not necessarily clearer.
Conway's Game of Life in one line:
http://www.catpad.net/michael/apl/
--
Steven D'Aprano
Lie Ryan
> On Wed, 9 Sep 2009 07:46:09 am Scott David Daniels wrote:
>> APL was one language that battered me over the head with the
>> proof that shorter was not necessarily clearer.
>
> Conway's Game of Life in one line:
>
> http://www.catpad.net/michael/apl/
Here is a hypothesis:
"The length of a code is inversely proportional to the length of
documentation required to explain the code"
The APL Conway's Game of Life requires a full page of documentation to
explain how it works. Most implementations of the same game have much
less documentation and much longer code.
Prove or disprove the hypothesis.
If proven true, the hypothesis may lead to:
The net worth of having a short, succinct code may be outweighed by the
amount of documentation needed to explain the code.
George Sakkis
> Steven D'Aprano wrote:
>>
>> On Wed, 9 Sep 2009 07:46:09 am Scott David Daniels wrote:
>>>
>>> APL was one language that battered me over the head with the
>>> proof that shorter was not necessarily clearer.
>>
>> Conway's Game of Life in one line:
>>
>> http://www.catpad.net/michael/apl/
>
>
> Here is a hypothesis:
> "The length of a code is inversely proportional to the length of
> documentation required to explain the code"
>
> The APL Conway's Game of Life requires a full page of documentation to
> explain how it works. Most implementations of the same game have much less
> documentation and much longer code.
>
> Prove or disprove the hypothesis.
>
> If proven true, the hypothesis may lead to:
> The net worth of having a short, succinct code may be outweighed by the
> amount of documentation needed to explain the code.
Any such proof or even discussion should take into account what the
primitives (atoms and allowed operations) are. If not, here is a
solution that is short both in code and documentation:
game_of_life().solve()
;-)
George
Greg Ewing
> Any such proof or even discussion should take into account what the
> primitives (atoms and allowed operations) are.
Probably you should include the size of the documentation
of the primitives used in your programming language
manual, any other well-known literature they implicitly
refer to, etc.
> If not, here is a
> solution that is short both in code and documentation:
>
> game_of_life().solve()
But then you need to go and find a paper describing
the game of life and the algorithm being used to
solve it and include its length!
--
Greg
