Re: Postfix conditionals
GöktuğKayaalp s...@gkayaalp.com wrote in message news:mailman.6377.1391490975.18130.python-l...@python.org... BartC b...@freeuk.com writes: Göktuğ Kayaalp s...@gkayaalp.com wrote in message news:mailman.4966.1388953508.18130.python-l...@python.org... AFAIK, we do not have postfix conditionals in Python, i.e. a condition appended to a statement, which determines whether the statement runs or not: py for i in [False]: ... break if not i What are your thoughts on this? I develop my own language (not Python, but also dynamic and interpreted). (First, some apologies; I thought the OP was dated February not January!) Would love to see that, if possible! (If you're into Python, then I doubt it because I don't have classes or any of those other Pythonic things that people like. However my language is a lot less dynamic and therefore can be much faster. I have a few interesting variations on statements as well; syntax is cheap and I don't know why many languages, Python included, have such a paucity of control and selection statements. I also have a project that translates my syntax into Python; the intention there was to be able to make use of some of its libraries because I don't have many of my own!) I have this feature, and it's OK, but not indispensible. I varied it a bit by allowing 'if', 'when' and 'unless' as the conditionals, just to break it up a little. However, it just maps internally to a regular if-statement. In Python though, the normal way of writing 'break if not i' is about the same length (in my language it's somewhat longer), so I can't see it getting much support. I do not really think that string length is not of much significance. The actual fact that disallows my proposal from being favoured/implemented is that in Python, `break', `return' and `continue' are statements and the community encourages having one statement per line, so that the source code is easily understandable. With my proposal implemented, the language would would be encouraging having multiple statements in one line, that looks like a single statement, but is indeed a composition of two. But, Python already allows you to combine two statements on a line, as in: if a: s while b: t So your: s if a is little different (although s will need to be restricted; 'if b if a' will look a bit odd). And someone mentioned the ternary expression which looks similar to your proposal. I suppose you can also argue that the if-part is not a statement at all, just an expression that is part of the statement (you'd have to redefine break and other statements to have an optional condition). If written as: break(not i) then it certainly won't look like two statements! Your proposal has the advantage in that it gives more dominance to the statement, making the code somewhat clearer, comparing with burying it inside an if-statement. I rather dislike the statement-orientedness of Python, but still, it is a good device of easening for the language developers and beginners when the fact that we use indentation to denote blocks is considered. (I used to have a syntax where statements and expressions were interchangeable. Now I have them distinct, which makes many things much easier, it picks up more errors (and makes it simpler to translate to translate into languages which aren't quite as expressive!)) -- Bartc -- https://mail.python.org/mailman/listinfo/python-list
Re: Postfix conditionals
Göktuğ Kayaalp s...@gkayaalp.com wrote in message news:mailman.4966.1388953508.18130.python-l...@python.org... AFAIK, we do not have postfix conditionals in Python, i.e. a condition appended to a statement, which determines whether the statement runs or not: py for i in [False]: ... break if not i The above piece of code is equivalent to this in Python: py for i in [False]: ...if not i ...break What are your thoughts on this? I develop my own language (not Python, but also dynamic and interpreted). I have this feature, and it's OK, but not indispensible. I varied it a bit by allowing 'if', 'when' and 'unless' as the conditionals, just to break it up a little. However, it just maps internally to a regular if-statement. In Python though, the normal way of writing 'break if not i' is about the same length (in my language it's somewhat longer), so I can't see it getting much support. What would be far more useful would be a proper 'switch' statement, but if that's not in, then I don't think your proposal will get far! (There are various clunky workarounds for switch - one idea is to use an if-elseif chain, but that's just what it tries to avoid. Switch is attractive for an interpreted language because - provided all cases are constants, a bit of a problem in Python, because as soon as you give a name to something, it's no longer constant - it can be implemented very efficiently.) -- Bartc -- https://mail.python.org/mailman/listinfo/python-list
Re: Postfix conditionals
[comments inline] BartC b...@freeuk.com writes: Göktuğ Kayaalp s...@gkayaalp.com wrote in message news:mailman.4966.1388953508.18130.python-l...@python.org... AFAIK, we do not have postfix conditionals in Python, i.e. a condition appended to a statement, which determines whether the statement runs or not: py for i in [False]: ... break if not i The above piece of code is equivalent to this in Python: py for i in [False]: ...if not i ...break What are your thoughts on this? I develop my own language (not Python, but also dynamic and interpreted). Would love to see that, if possible! I have this feature, and it's OK, but not indispensible. I varied it a bit by allowing 'if', 'when' and 'unless' as the conditionals, just to break it up a little. However, it just maps internally to a regular if-statement. In Python though, the normal way of writing 'break if not i' is about the same length (in my language it's somewhat longer), so I can't see it getting much support. I do not really think that string length is not of much significance. The actual fact that disallows my proposal from being favoured/implemented is that in Python, `break', `return' and `continue' are statements and the community encourages having one statement per line, so that the source code is easily understandable. With my proposal implemented, the language would would be encouraging having multiple statements in one line, that looks like a single statement, but is indeed a composition of two. I rather dislike the statement-orientedness of Python, but still, it is a good device of easening for the language developers and beginners when the fact that we use indentation to denote blocks is considered. What would be far more useful would be a proper 'switch' statement, but if that's not in, then I don't think your proposal will get far! (There are various clunky workarounds for switch - one idea is to use an if-elseif chain, but that's just what it tries to avoid. Switch is attractive for an interpreted language because - provided all cases are constants, a bit of a problem in Python, because as soon as you give a name to something, it's no longer constant - it can be implemented very efficiently.) -- Bartc -- https://mail.python.org/mailman/listinfo/python-list
Re: Postfix conditionals
On Tue, Feb 4, 2014 at 4:16 PM, Göktuğ Kayaalp s...@gkayaalp.com wrote: With my proposal implemented, the language would would be encouraging having multiple statements in one line, that looks like a single statement, but is indeed a composition of two. I wouldn't have a problem with if not i: break in Python, as long as the condition is short. In something that reads from a socket until the other end closes, for instance, I'm fine with this: while True: data = sock.read(1024) if not data: break do_stuff_with(data) which will stop as soon as sock.read() returns , which it does when the other end is gone. (I wrote something doing exactly this today, and did exactly this. Probably could have made the code a bit simpler if I could depend on Python 3.3, but it has to run on 2.7 and maybe 2.6 so I had to stick with their facilities.) Yes, it's two statements, but a list comprehension is a whole pile of statement-y things, and that's usually a single line. If it's doing one conceptual action, it's okay to not split it. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
Re: Postfix conditionals
On Mon, 06 Jan 2014 07:51:28 -, Göktuğ Kayaalp s...@gkayaalp.com wrote: Thanks for the input! I'd be quite interested in examples which required you to mentally transpose the conditional back to the start of the statement, by the way. Sorry, it's been too long and I don't have any relevant Perl around any more. I think it had to do with losing the visual cue of indentation, and just having to think that little bit harder to notice that I wasn't dealing with purely linear code. -- Rhodri James *-* Wildebeest Herder to the Masses -- https://mail.python.org/mailman/listinfo/python-list
Re: Postfix conditionals
In article mailman.4966.1388953508.18130.python-l...@python.org, Göktu⬠Kayaalp s...@gkayaalp.com wrote: py for i in [False]: ... break if not i Python is not Perl. -- https://mail.python.org/mailman/listinfo/python-list
Re: Postfix conditionals
On 05-01-2014 22:41, Roy Smith wrote: In article mailman.4966.1388953508.18130.python-l...@python.org, Göktu€ Kayaalp s...@gkayaalp.com wrote: py for i in [False]: ... break if not i Python is not Perl. Well done! Good for you, that you know the fact; but you are not being constructive. Python is not C either, but we have the while loop. Python is not Smalltalk, but we have classes. Python is not LISP, but we have function literals. Hopefully Guido did not have your approach back when he created Python, or we'd have an assembly language or something instead today. -- https://mail.python.org/mailman/listinfo/python-list
Re: Postfix conditionals
On Sun, Jan 5, 2014 at 12:41 PM, Roy Smith r...@panix.com wrote: In article mailman.4966.1388953508.18130.python-l...@python.org, Göktu€ Kayaalp s...@gkayaalp.com wrote: py for i in [False]: ... break if not i Python is not Perl. Personally, I find the suggested syntax jarring. I'd prefer that it not go into Python. -- https://mail.python.org/mailman/listinfo/python-list
Re: Postfix conditionals
On Sun, Jan 5, 2014 at 12:24 PM, Göktuğ Kayaalp s...@gkayaalp.com wrote:
Hi,
AFAIK, we do not have postfix conditionals in Python, i.e. a condition
appended to a
statement, which determines whether the statement runs or not:
py for i in [False]:
... break if not i
The above piece of code is equivalent to this in Python:
py for i in [False]:
...if not i
...break
I believe that the first example is superior to the second example when the
two is compared
for readability and intuitiveness.
I'm going to have to disagree. I dislike how this obscures the
if-statement, complicates the language grammar, and adds another
unnecessary way to express the same thing (which violates TOOWTDI)
with little countervailing benefit.
We already have a ternary statement that
looks similar,
py print('hi') if True else None
Actually, to be pedantic, it's a ternary *expression*. Using it purely
for side-effects (i.e. as a statement) is rather unidiomatic, in the
same way that abusing list comprehensions, e.g.:
[print(i) for i in range(42)]
is frowned upon.
Not to mention that the ternary doesn't work for actual statements
(print() is just a function call in Python 3):
(x = 1) if True else (x = 2)
File stdin, line 1
(x = 1) if True else (x = 2)
^
SyntaxError: invalid syntax
so I reckon there would be no breakage in old code if this kind of syntax
was added. Ruby has
this, and AFAIK Perl also does.
I lack the knowledge of whether the community has opinions on this kind of
notation, so I am
posting this here instead of the ideas list. What are your thoughts on
this?
You can already write:
for i in [False]:
if not i: break
if you feel the need for terseness or a one-liner. Perhaps this
satisfies your desire?
Cheers,
Chris
--
https://mail.python.org/mailman/listinfo/python-list
Fwd: Re: Postfix conditionals
This was sent to me as a private reply to a question that I have posted
to python-list@python.org, so I am forwarding it to here.
Chris, please send your messages to the list, and cc the OP.
Original Message
Subject:Re: Postfix conditionals
Date: Sun, 5 Jan 2014 14:09:14 -0800
From: Chris Rebert c...@rebertia.com
To: Göktuğ Kayaalp s...@gkayaalp.com
CC: Python python-list@python.org
On Sun, Jan 5, 2014 at 12:24 PM, Göktuğ Kayaalp s...@gkayaalp.com wrote:
Hi,
AFAIK, we do not have postfix conditionals in Python, i.e. a condition
appended to a
statement, which determines whether the statement runs or not:
py for i in [False]:
... break if not i
The above piece of code is equivalent to this in Python:
py for i in [False]:
...if not i
...break
I believe that the first example is superior to the second example when the
two is compared
for readability and intuitiveness.
I'm going to have to disagree. I dislike how this obscures the
if-statement, complicates the language grammar, and adds another
unnecessary way to express the same thing (which violates TOOWTDI)
with little countervailing benefit.
We already have a ternary statement that
looks similar,
py print('hi') if True else None
Actually, to be pedantic, it's a ternary *expression*. Using it purely
for side-effects (i.e. as a statement) is rather unidiomatic, in the
same way that abusing list comprehensions, e.g.:
[print(i) for i in range(42)]
is frowned upon.
Not to mention that the ternary doesn't work for actual statements
(print() is just a function call in Python 3):
(x = 1) if True else (x = 2)
File stdin, line 1
(x = 1) if True else (x = 2)
^
SyntaxError: invalid syntax
so I reckon there would be no breakage in old code if this kind of syntax
was added. Ruby has
this, and AFAIK Perl also does.
I lack the knowledge of whether the community has opinions on this kind of
notation, so I am
posting this here instead of the ideas list. What are your thoughts on
this?
You can already write:
for i in [False]:
if not i: break
if you feel the need for terseness or a one-liner. Perhaps this
satisfies your desire?
Cheers,
Chris
--
https://mail.python.org/mailman/listinfo/python-list
Re: Re: Postfix conditionals
On Sun, Jan 5, 2014 at 2:12 PM, Göktuğ Kayaalp s...@gkayaalp.com wrote: This was sent to me as a private reply No, it was sent as a public reply via Reply-All; note that python-list was CC-ed, which works just fine: https://mail.python.org/pipermail/python-list/2014-January/663858.html to a question that I have posted to python-list@python.org, so I am forwarding it to here. snip Original Message Subject: Re: Postfix conditionals Date: Sun, 5 Jan 2014 14:09:14 -0800 From: Chris Rebert c...@rebertia.com To: Göktuğ Kayaalp s...@gkayaalp.com CC: Python python-list@python.org message body snipped because there's no need for a third redundant copy of my message -- https://mail.python.org/mailman/listinfo/python-list
Re: Postfix conditionals
On Sun, 05 Jan 2014 20:24:53 -, Göktuğ Kayaalp s...@gkayaalp.com wrote: AFAIK, we do not have postfix conditionals in Python, i.e. a condition appended to a statement, which determines whether the statement runs or not: py for i in [False]: ... break if not i The above piece of code is equivalent to this in Python: py for i in [False]: ...if not i ...break I believe that the first example is superior to the second example when the two is compared for readability and intuitiveness. In my past life as a newcomer to Perl, I thought this too. Postfix conditionals read more like English, so they would be easier to take in and understand. As I wrote more code, I discovered that this didn't seem to be the case; except in very simple cases, I had to mentally transpose the conditional back to the start of the statement to properly comprehend what was going on and what the results would be for my sample data. It looks like a good idea, but I don't think it works that well in practice. -- Rhodri James *-* Wildebeest Herder to the Masses -- https://mail.python.org/mailman/listinfo/python-list
Re: Postfix conditionals
On 1/5/2014 3:24 PM, Göktuğ Kayaalp wrote:
Hi,
AFAIK, we do not have postfix conditionals in Python, i.e. a condition
appended to a
statement, which determines whether the statement runs or not:
py for i in [False]:
... break if not i
The above piece of code is equivalent to this in Python:
py for i in [False]:
...if not i
...break
I believe that the first example is superior to the second example when
the two is compared
for readability and intuitiveness. We already have a ternary statement
'conditional expression', which happens to be a ternary as opposed to
binary expression.
that looks similar,
py print('hi') if True else None
so I reckon there would be no breakage in old code if this kind of
syntax was added. Ruby has
this, and AFAIK Perl also does.
I lack the knowledge of whether the community has opinions on this kind
of notation,
In general, negative on pure duplication. Guido has said he strongly
dislikes the perl reverse if.
--
Terry Jan Reedy
--
https://mail.python.org/mailman/listinfo/python-list
Re: Postfix conditionals
On 06-01-2014 03:40, Rhodri James wrote: On Sun, 05 Jan 2014 20:24:53 -, Göktuğ Kayaalp s...@gkayaalp.com wrote: AFAIK, we do not have postfix conditionals in Python, i.e. a condition appended to a statement, which determines whether the statement runs or not: py for i in [False]: ... break if not i The above piece of code is equivalent to this in Python: py for i in [False]: ...if not i ...break I believe that the first example is superior to the second example when the two is compared for readability and intuitiveness. In my past life as a newcomer to Perl, I thought this too. Postfix conditionals read more like English, so they would be easier to take in and understand. As I wrote more code, I discovered that this didn't seem to be the case; except in very simple cases, I had to mentally transpose the conditional back to the start of the statement to properly comprehend what was going on and what the results would be for my sample data. It looks like a good idea, but I don't think it works that well in practice. Thanks for the input! I'd be quite interested in examples which required you to mentally transpose the conditional back to the start of the statement, by the way. gk -- https://mail.python.org/mailman/listinfo/python-list
