do/while structure needed

[John Salerno]

1 random.shuffle( letters)
2 trans_letters = ''.join(letters )[:len(original_s et)]
3 trans_table = string.maketran s(original_set, trans_letters)

So what I'd like to do is have lines 1 and 2 run once, then I want to do
some comparison between original_set and trans_letters before running
line 3. If the comparison passes, line 3 runs; otherwise, lines 1 and 2
run again.

A do/while would be good for this, but perhaps I'm looking at it in the
wrong way? Or is there some kind of do/while type of idiom that I could use?

Thanks.

[George Sakkis]

Re: do/while structure needed

John Salerno wrote:
[color=blue]
> 1 random.shuffle( letters)
> 2 trans_letters = ''.join(letters )[:len(original_s et)]
> 3 trans_table = string.maketran s(original_set, trans_letters)
>
> So what I'd like to do is have lines 1 and 2 run once, then I want to do
> some comparison between original_set and trans_letters before running
> line 3. If the comparison passes, line 3 runs; otherwise, lines 1 and 2
> run again.
>
> A do/while would be good for this, but perhaps I'm looking at it in the
> wrong way? Or is there some kind of do/while type of idiom that I could use?
>
> Thanks.[/color]

I guess you want something like:

while True:
random.shuffle( letters)
trans_letters = ''.join(letters )[:len(original_s et)]
if some_compatison (original_set,t rans_letters):
trans_table = string.maketran s(original_set, trans_letters)
break


HTH,
George

[Ten]

Re: do/while structure needed

On Sunday 14 May 2006 06:17, John Salerno wrote:[color=blue]
> 1 random.shuffle( letters)
> 2 trans_letters = ''.join(letters )[:len(original_s et)]
> 3 trans_table = string.maketran s(original_set, trans_letters)
>
> So what I'd like to do is have lines 1 and 2 run once, then I want to do
> some comparison between original_set and trans_letters before running
> line 3. If the comparison passes, line 3 runs; otherwise, lines 1 and 2
> run again.
>
> A do/while would be good for this, but perhaps I'm looking at it in the
> wrong way? Or is there some kind of do/while type of idiom that I could
> use?
>
> Thanks.[/color]

while not comparison(orig inal_set, trans_letters):
random.shuffle( letters)
trans_letters = ''.join(letters )[:len(original_s et)]

trans_table = string.maketran s(original_set, trans_letters)

HTH,

Ten

--
There are 10 types of people in this world,
those who understand binary, and those who don't.

[Paul McGuire]

Re: do/while structure needed


"Ten" <runlevelten@gm ail.com> wrote in message
news:mailman.56 77.1147617486.2 7775.python-list@python.org ...[color=blue]
> On Sunday 14 May 2006 06:17, John Salerno wrote:[color=green]
> > 1 random.shuffle( letters)
> > 2 trans_letters = ''.join(letters )[:len(original_s et)]
> > 3 trans_table = string.maketran s(original_set, trans_letters)
> >
> > So what I'd like to do is have lines 1 and 2 run once, then I want to do
> > some comparison between original_set and trans_letters before running
> > line 3. If the comparison passes, line 3 runs; otherwise, lines 1 and 2
> > run again.
> >
> > A do/while would be good for this, but perhaps I'm looking at it in the
> > wrong way? Or is there some kind of do/while type of idiom that I could
> > use?
> >
> > Thanks.[/color]
>
> while not comparison(orig inal_set, trans_letters):
> random.shuffle( letters)
> trans_letters = ''.join(letters )[:len(original_s et)]
>
> trans_table = string.maketran s(original_set, trans_letters)
>[/color]

I don't think the OP wants to call comparison until after the first pass
through the loop. Here's a modification to your version that skips the
comparison test on the first pass:

first = True
while first or not comparison(orig inal_set, trans_letters):
first = False
random.shuffle( letters)
trans_letters = ''.join(letters )[:len(original_s et)]

trans_table = string.maketran s(original_set, trans_letters)


-- Paul

[John Salerno]

Re: do/while structure needed

George Sakkis wrote:
[color=blue]
> while True:
> random.shuffle( letters)
> trans_letters = ''.join(letters )[:len(original_s et)]
> if some_compatison (original_set,t rans_letters):
> trans_table = string.maketran s(original_set, trans_letters)
> break[/color]

Thanks, that looks pretty good. Although I have to say, a do/while
structure is the much more obvious way. I wonder why it hasn't been
added to the language.

[Terry Reedy]

Re: do/while structure needed


"John Salerno" <johnjsal@NOSPA Mgmail.com> wrote in message
news:4467786c$0 $1956$c3e8da3@n ews.astraweb.co m...[color=blue]
> Thanks, that looks pretty good. Although I have to say, a do/while
> structure is the much more obvious way. I wonder why it hasn't been
> added to the language.[/color]

Been suggested many times, been considered, and rejected. Easily similated
with while True: ... if exit_condition: break which also solves 'loop and a
half' problem, which is more common. Requires new keyword for little gain.
Etc.

tjr

[John Salerno]

Re: do/while structure needed

Terry Reedy wrote:[color=blue]
> "John Salerno" <johnjsal@NOSPA Mgmail.com> wrote in message
> news:4467786c$0 $1956$c3e8da3@n ews.astraweb.co m...[color=green]
>> Thanks, that looks pretty good. Although I have to say, a do/while
>> structure is the much more obvious way. I wonder why it hasn't been
>> added to the language.[/color]
>
> Been suggested many times, been considered, and rejected. Easily similated
> with while True: ... if exit_condition: break which also solves 'loop and a
> half' problem, which is more common. Requires new keyword for little gain.
> Etc.[/color]

I know, I remember a discussion about it a while back. But IMO, at
least, a do/while structure seems much cleaner and more readable than a
while loop with an embedded if and break statement.

[Antoon Pardon]

Re: do/while structure needed

Op 2006-05-15, Terry Reedy schreef <tjreedy@udel.e du>:[color=blue]
>
> "John Salerno" <johnjsal@NOSPA Mgmail.com> wrote in message
> news:4467786c$0 $1956$c3e8da3@n ews.astraweb.co m...[color=green]
>> Thanks, that looks pretty good. Although I have to say, a do/while
>> structure is the much more obvious way. I wonder why it hasn't been
>> added to the language.[/color]
>
> Been suggested many times, been considered, and rejected. Easily similated
> with while True: ... if exit_condition: break which also solves 'loop and a
> half' problem, which is more common. Requires new keyword for little gain.
> Etc.[/color]

It isn't rejected. PEP 315 is only deferred. Which as far as I
understand means it is postponed because other things seemed
more important.

--
Antoon Pardon

[John Salerno]

Re: do/while structure needed

Dennis Lee Bieber wrote:
[color=blue]
> And what syntax would you propose?[/color]

I guess something like:


do:
stuff goes here
and here
and here
while (condition)


The absence of a colon after the while statement can be the signal that
it isn't a regular while statement with a following block, but instead
the final statement of a do/while loop. Or would that cause an issue?

[Edward Elliott]

Re: do/while structure needed

Dennis Lee Bieber wrote:
[color=blue]
> Would you put the condition at the top of the loop -- and confuse
> those people who believe the exit condition should appear at the point
> the exit activates?[/color]

Confusion is not the issue. You can put the condition smack dab in the
middle of the loop, as long as the location is consistent people will know
where to look for it. Rejecting because "some are confused the first time
since other languages do it differently" gets you nowhere: some group will
always be confused by something. They learn, problem solved.

I agree that do/while is unnecessary. But I'd argue against it on grounds
of simplicity and readability instead of confusion.

--
Edward Elliott
UC Berkeley School of Law (Boalt Hall)
complangpython at eddeye dot net