Re: [Python-Dev] conditional expressions - add parens?
On 3/11/06, Joe Smith [EMAIL PROTECTED] wrote: Well the original was almost certainly a tongue-in-cheek reference to LISP. LISP was a disaster to use, so I doubt your language would have been any worse. The way one identifies a lisp programmer is to find the person whose paren keys have worn competely off their keyboard. :D Given how much Python is indebted to Lisp, digs at Lisp seem particularly off-topic for this list. Fully expecting this to bounce, -- --Guido van Rossum (home page: http://www.python.org/~guido/) ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] conditional expressions - add parens?
Joe Smith wrote: LISP was a disaster to use, so I doubt your language would have been any worse. At least Lisp would let you say (* 4 a c) and not force you to write (* (* 4 a) c) My language would not have been so forgiving, unless you were willing to define a bunch of different * functions with different numbers of parameters. BTW, I did use Lisp and Scheme fairly heavily for a period, and didn't find them to be disasters -- at least not because of the parens. Greg ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] conditional expressions - add parens?
Greg Ewing [EMAIL PROTECTED] wrote in message news:[EMAIL PROTECTED] Jeremy Hylton wrote: Perhaps the solution is to require parens around all expressions, a simple consistent rule. I actually designed a language with that feature once. It was an exercise in minimality, with hardly anything built-in -- all the arithmetic operators, etc. were defined in the language. A result was that there was no built-in notion of precedence, and my solution was to require parentheses around every infix operation. So instead of dsq = b * b - 4 * a * c you would have had to write dsq = ((b * b) - ((4 * a) * c)) I never got an implementation working well enough to find out how much of a disaster this would have been to use, though. :-) Well the original was almost certainly a tongue-in-cheek reference to LISP. LISP was a disaster to use, so I doubt your language would have been any worse. The way one identifies a lisp programmer is to find the person whose paren keys have worn competely off their keyboard. :D ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] conditional expressions - add parens?
Morel Xavier wrote: Steve Holden wrote: Contrast with the bleeding obvious: level = 0 if absolute_import in self.futures: level = -1 regards Steve The issue that spawned the necessity of a ternary operator in the first place was that this syntax is not usable at all in quite a few situations like, say, list comprehensions... And of course the example I criticized was a list comprehension (not). The fact that ternary operators improve some features isn't an excuse for using them when they actually decrease readability. regards Steve -- Steve Holden +44 150 684 7255 +1 800 494 3119 Holden Web LLC/Ltd www.holdenweb.com Love me, love my blog holdenweb.blogspot.com ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] conditional expressions - add parens?
Steve Holden wrote: Contrast with the bleeding obvious: level = 0 if absolute_import in self.futures: level = -1 regards Steve The issue that spawned the necessity of a ternary operator in the first place was that this syntax is not usable at all in quite a few situations like, say, list comprehensions... ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] conditional expressions - add parens?
Joe Smith wrote:
Steve Holden [EMAIL PROTECTED] wrote in message
news:[EMAIL PROTECTED]
Jim Jewett wrote:
I think that adding parentheses would help, by at least signalling that
the logic is longer than just the next (single) expression.
level = (0 if absolute_import in self.futures else -1)
Contrast with the bleeding obvious:
level = 0
if absolute_import in self.futures:
level = -1
or even, if a certain obscurity is desirable:
level = - (absolute_import in self.futures)
Wait a second.
I may be just a user but if the above is correct then that syntax needs to
die!
There is no logical reason for XX if YY else ZZ to be roughly equivlent
to:
if (YY) then {ZZ} else {XX} , but AFAICT that is pretty much the way you
expanded that.
I hope I misunderstood, or that there was a typo in a post.
There was a typo in the post.
regards
Steve
--
Steve Holden +44 150 684 7255 +1 800 494 3119
Holden Web LLC/Ltd www.holdenweb.com
Love me, love my blog holdenweb.blogspot.com
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Re: [Python-Dev] conditional expressions - add parens?
On 3/6/06, Alex Martelli [EMAIL PROTECTED] wrote: On Mar 6, 2006, at 9:17 AM, Jim Jewett wrote: ... I think that adding parentheses would help, by at least signalling that the logic is longer than just the next (single) expression. level = (0 if absolute_import in self.futures else -1) +1 (just because I can't give it +3.1415926...!!!). *Mandatory* parentheses make this form MUCH more readable. Recent language features seem to be suffereing from excessive parenthesisitis. I worry that people will stop remembering which expressions requirement parens in which context. Perhaps the solution is to require parens around all expressions, a simple consistent rule. If so, then adding parens around all statements is a fairly natural extension, which solves a number of problems like how to make a richer lambda. Jeremy ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] conditional expressions - add parens?
On 3/7/06, Jeremy Hylton [EMAIL PROTECTED] wrote: On 3/6/06, Alex Martelli [EMAIL PROTECTED] wrote: On Mar 6, 2006, at 9:17 AM, Jim Jewett wrote: ... I think that adding parentheses would help, by at least signalling that the logic is longer than just the next (single) expression. level = (0 if absolute_import in self.futures else -1) +1 (just because I can't give it +3.1415926...!!!). *Mandatory* parentheses make this form MUCH more readable. Recent language features seem to be suffereing from excessive parenthesisitis. Agreed. Mandatory parentheses purely for readability are ultimately futile - I bet I can write unreadable code even if the parens were required :-) The parentheses around genexps were (AFAICT) different - without them, the grammar was ambiguous, so some way of disambiguating was needed. +0 for mentioning parens around conditional expressions in PEP 8. But it's aready covered by the general code should be readable in my view. Paul. ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] conditional expressions - add parens?
Paul Moore wrote: On 3/7/06, Jeremy Hylton [EMAIL PROTECTED] wrote: On 3/6/06, Alex Martelli [EMAIL PROTECTED] wrote: On Mar 6, 2006, at 9:17 AM, Jim Jewett wrote: ... I think that adding parentheses would help, by at least signalling that the logic is longer than just the next (single) expression. level = (0 if absolute_import in self.futures else -1) +1 (just because I can't give it +3.1415926...!!!). *Mandatory* parentheses make this form MUCH more readable. Recent language features seem to be suffereing from excessive parenthesisitis. Agreed. Mandatory parentheses purely for readability are ultimately futile - I bet I can write unreadable code even if the parens were required :-) The parentheses around genexps were (AFAICT) different - without them, the grammar was ambiguous, so some way of disambiguating was needed. +0 for mentioning parens around conditional expressions in PEP 8. But it's aready covered by the general code should be readable in my view. Agreed - and often the best way to make a conditional expression readable is to not use it in the first place, which is a concept that an official policy on parentheses may mask. And then there's the question of how to parenthesise chained conditional expressions. Mandatory parentheses in that case would make me wonder if I was writing a certain language that isn't Python. . . Given that the main reason PEP 308 was finally implemented was to provide OOWTDI for conditional expressions (instead of the handful of not-at-all-obvious and not-quite-right-either workarounds that had developed in their absence), I expect to see of rush of enthusiastic overuse of the new expression, which will eventually settle down as everyone remembers that not every problem is a nail to be hit with the shiny new hammer ;) Cheers, Nick. -- Nick Coghlan | [EMAIL PROTECTED] | Brisbane, Australia --- http://www.boredomandlaziness.org ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] conditional expressions - add parens?
On 3/7/06, Paul Moore [EMAIL PROTECTED] wrote: The parentheses around genexps were (AFAICT) different - without them, the grammar was ambiguous, so some way of disambiguating was needed. The out-of-order evaluation is a very large change, because now we have a situation where normal parsing completes an expression, but needs to avoid evaluating it, just in case. Currently, we can write: if False: print r else: print 6 6 r Traceback (most recent call last): File pyshell#14, line 1, in -toplevel- r NameError: name 'r' is not defined In the above example, r doesn't get evaluated because the if ahead of it says to skip that branch. But with conditional expressions, that flow control is changed from *later* in the program. I don't think we'll see the equivalent of Intercal Suck Points anywhere but intentionally obfuscated code, but I do expect to see: side_effect() if condition In fact, I think the below examples are reasonable uses that do a better job of expressing intent than the if statement would. I just don't like the mental backtrack they require, and would like some sort of advance warning. Parentheses at least tell me You're not done yet; keep reading. ack(r,r) if r not in cache log(message) if error_flag -jJ ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] conditional expressions - add parens?
Jim Jewett wrote: On 3/7/06, Paul Moore [EMAIL PROTECTED] wrote: The parentheses around genexps were (AFAICT) different - without them, the grammar was ambiguous, so some way of disambiguating was needed. The out-of-order evaluation is a very large change, because now we have a situation where normal parsing completes an expression, but needs to avoid evaluating it, just in case. Currently, we can write: if False: print r else: print 6 6 r Traceback (most recent call last): File pyshell#14, line 1, in -toplevel- r NameError: name 'r' is not defined In the above example, r doesn't get evaluated because the if ahead of it says to skip that branch. But with conditional expressions, that flow control is changed from *later* in the program. I don't think we'll see the equivalent of Intercal Suck Points anywhere but intentionally obfuscated code, but I do expect to see: side_effect() if condition In fact, I think the below examples are reasonable uses that do a better job of expressing intent than the if statement would. I just don't like the mental backtrack they require, and would like some sort of advance warning. Parentheses at least tell me You're not done yet; keep reading. ack(r,r) if r not in cache log(message) if error_flag I think you've misunderstood the nature of the change. HTe new conditionals are *expressions*, they aren't postfix conditionals for statements. regards Steve -- Steve Holden +44 150 684 7255 +1 800 494 3119 Holden Web LLC/Ltd www.holdenweb.com Love me, love my blog holdenweb.blogspot.com ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] conditional expressions - add parens?
On Mar 7, 2006, at 7:29 AM, Steve Holden wrote: ... In fact, I think the below examples are reasonable uses that do a better job of expressing intent than the if statement would. I just don't like the mental backtrack they require, and would like some sort of advance warning. Parentheses at least tell me You're not done yet; keep reading. ack(r,r) if r not in cache log(message) if error_flag I think you've misunderstood the nature of the change. HTe new conditionals are *expressions*, they aren't postfix conditionals for statements. Right, but the only effect of that on the examples is that they both need an 'else None' continuation or thereabouts. I also predict widespread over-use of the new toy and agree with Jim that mandatory parentheses around the whole (X if Y else Z) construct would ameliorate legibility a bit. Alex ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] conditional expressions - add parens?
Paul Moore wrote: +0 for mentioning parens around conditional expressions in PEP 8. But it's aready covered by the general code should be readable in my view. Indeed. Writing readable code is ultimately the responsibility of the person doing the writing. It's enough that you *can* put parentheses around things if it helps readability. -- Greg Ewing, Computer Science Dept, +--+ University of Canterbury, | Carpe post meridiam! | Christchurch, New Zealand | (I'm not a morning person.) | [EMAIL PROTECTED] +--+ ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] conditional expressions - add parens?
Greg Ewing wrote: Jeremy Hylton wrote: Perhaps the solution is to require parens around all expressions, a simple consistent rule. I actually designed a language with that feature once. It was an exercise in minimality, with hardly anything built-in -- all the arithmetic operators, etc. were defined in the language. A result was that there was no built-in notion of precedence, and my solution was to require parentheses around every infix operation. So instead of dsq = b * b - 4 * a * c you would have had to write dsq = ((b * b) - ((4 * a) * c)) I never got an implementation working well enough to find out how much of a disaster this would have been to use, though. :-) I already do that anyway, and even update other people's code in any open-source projects I contribute to, because I find it *far* easier to read and write 'unnecessary' parens than remember precedence rules. But I can understand why some people would balk at it, so +0.5 from me. ;) Robert Brewer System Architect Amor Ministries [EMAIL PROTECTED] ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
[Python-Dev] conditional expressions - add parens?
Now that we have started to see conditional expressions ... I would like to see them parenthesized. The parens aren't as important as they are with generator expressions, but ... they matter.From a recent checkin -- level = 0 if absolute_import in self.futures else -1Mentally, I can't help parsing that as level = 0 plus comments that turn out to be code that triggers backracking.When the expressions (particularly the true case) are longer, it gets even worse. I think that adding parentheses would help, by at least signalling that the logic is longer than just the next (single) _expression_.level = (0 if absolute_import in self.futures else -1) -jJ ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] conditional expressions - add parens?
On 3/6/06, Jim Jewett [EMAIL PROTECTED] wrote: From a recent checkin -- level = 0 if absolute_import in self.futures else -1Mentally, I can't help parsing that as level = 0 plus comments that turn out to be code that triggers backracking.When the expressions (particularly the true case) are longer, it gets even worse. I think that adding parentheses would help, by at least signalling that the logic is longer than just the next (single) _expression_.level = (0 if absolute_import in self.futures else -1) I'm not sure, are you suggesting the grammar/parser enforces it that way, or that it should be in PEP-8?(I still can't help but go 'yecchh' whenever I see the code. It looks like Perl's 'expr if expr' form, but it behaves quite different. Right now, removing if/else expressions still looks like the best solution, to me :- But gauging reactions (my own and others) to the actual if-expr in use is the main reason I added those couple of lines to the compiler package.) -- Thomas Wouters [EMAIL PROTECTED]Hi! I'm a .signature virus! copy me into your .signature file to help me spread! ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] conditional expressions - add parens?
On 3/6/06, Thomas Wouters [EMAIL PROTECTED] wrote: On 3/6/06, Jim Jewett [EMAIL PROTECTED] wrote: level = 0 if absolute_import in self.futures else -1 Mentally, I can't help parsing that as level = 0 plus comments that turn out to be code that triggers backtracking. I think that adding parentheses would help ... level = (0 if absolute_import in self.futures else -1) I'm not sure, are you suggesting the grammar/parser enforces it that way, or that it should be in PEP-8? I would prefer that the grammar enforce it, but putting it in PEP 8 would be a half-way measure. I can't imagine an expression small enough that the parentheses really hurt. var = t if c else f var = (t if c else f) In PEP 8, I would even go so far as to recommend parentheses around the three sub-expressions if they contain any internal whitespace, but I don't think the grammar should enforce that. (I still can't help but go 'yecchh' whenever I see the code. It looks like Perl's 'expr if expr' form, but it behaves quite different. Right now, removing if/else expressions still looks like the best solution, to me :- Yah, that sounds uncontroversial. :D -jJ ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] conditional expressions - add parens?
Jim Jewett wrote: Now that we have started to see conditional expressions ... I would like to see them parenthesized. The parens aren't as important as they are with generator expressions, but ... they matter. From a recent checkin -- level = 0 if absolute_import in self.futures else -1 Personally I think the above code exemplifies exactly why Guido was correct in his reluctance to add conditional expressions. Mentally, I can't help parsing that as level = 0 plus comments that turn out to be code that triggers backracking. When the expressions (particularly the true case) are longer, it gets even worse. I think that adding parentheses would help, by at least signalling that the logic is longer than just the next (single) expression. level = (0 if absolute_import in self.futures else -1) Contrast with the bleeding obvious: level = 0 if absolute_import in self.futures: level = -1 or even, if a certain obscurity is desirable: level = - (absolute_import in self.futures) regards Steve -- Steve Holden +44 150 684 7255 +1 800 494 3119 Holden Web LLC/Ltd www.holdenweb.com Love me, love my blog holdenweb.blogspot.com ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] conditional expressions - add parens?
Morel Xavier wrote: Steve Holden wrote: Contrast with the bleeding obvious: level = 0 if absolute_import in self.futures: level = -1 regards Steve The issue that spawned the necessity of a ternary operator in the first place was that this syntax is not usable at all in quite a few situations like, say, list comprehensions... Sure, and for those uses it's good enough. This isn't really a python-dev topic, though, so I'll avoid following up further on this list. regards Steve -- Steve Holden +44 150 684 7255 +1 800 494 3119 Holden Web LLC/Ltd www.holdenweb.com Love me, love my blog holdenweb.blogspot.com ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] conditional expressions - add parens?
On Mar 6, 2006, at 9:17 AM, Jim Jewett wrote: ... I think that adding parentheses would help, by at least signalling that the logic is longer than just the next (single) expression. level = (0 if absolute_import in self.futures else -1) +1 (just because I can't give it +3.1415926...!!!). *Mandatory* parentheses make this form MUCH more readable. Alex ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] conditional expressions - add parens?
Steve Holden [EMAIL PROTECTED] wrote in message
news:[EMAIL PROTECTED]
Jim Jewett wrote:
I think that adding parentheses would help, by at least signalling that
the logic is longer than just the next (single) expression.
level = (0 if absolute_import in self.futures else -1)
Contrast with the bleeding obvious:
level = 0
if absolute_import in self.futures:
level = -1
or even, if a certain obscurity is desirable:
level = - (absolute_import in self.futures)
Wait a second.
I may be just a user but if the above is correct then that syntax needs to
die!
There is no logical reason for XX if YY else ZZ to be roughly equivlent
to:
if (YY) then {ZZ} else {XX} , but AFAICT that is pretty much the way you
expanded that.
I hope I misunderstood, or that there was a typo in a post.
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Re: [Python-Dev] conditional expressions - add parens?
[Jim Jewett]
I think that adding parentheses would help, by at least signalling that
the logic is longer than just the next (single) expression.
level = (0 if absolute_import in self.futures else -1)
[Steve Holden]
Contrast with the bleeding obvious:
level = 0
if absolute_import in self.futures:
level = -1
or even, if a certain obscurity is desirable:
level = - (absolute_import in self.futures)
In honor of Peter Naur receiving the 2005 Turing Award:
http://campus.acm.org/public/pressroom/press_releases/3_2006/turing_3_01_2006.cfm
and remembering Python's Algol roots, I'd like to constrast it with
the truly obvious:
level = (if absolute_import in self.futures then 0 else -1)
That way also has the minor advantage of computing the same value for
`level` as Jim's code ;-)
[Joe Smith]
Wait a second.
I may be just a user but if the above is correct then that syntax needs to
die!
There is no logical reason for XX if YY else ZZ to be roughly equivlent
to:
if (YY) then {ZZ} else {XX} , but AFAICT that is pretty much the way you
expanded that.
Ya, Steve just got it backwards. (X if Y else Z) is the same as
(if Y then X else Z), except for the excessive novelty. The obvious
spelling would require making then a keyword, which is actually OK
with everyone :-)
I hope I misunderstood, or that there was a typo in a post.
You were lucky this time, bucko, but don't ever go questioning a
python-dev regular again ;-)
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Re: [Python-Dev] conditional expressions - add parens?
Alex Martelli wrote: On Mar 6, 2006, at 9:17 AM, Jim Jewett wrote: ... I think that adding parentheses would help, by at least signalling that the logic is longer than just the next (single) expression. level = (0 if absolute_import in self.futures else -1) +1 (just because I can't give it +3.1415926...!!!). *Mandatory* parentheses make this form MUCH more readable. but which parens ? level = 0 if absolute_import in self.futures else -1 level = 0 if (absolute_import in self.futures) else -1 level = (0 if absolute_import in self.futures else -1) level = (0 if (absolute_import in self.futures) else -1) level = ((0) if (absolute_import in self.futures) else (-1)) # ... if you're asking me, I'd say that the second alternative is most readable here. at least as long as level = if (absolute_import in self.futures) then 0 else -1 is not on the list... level = 0 or -1 depending on absolute_import in self.futures /F ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
