define loop statement?

Re: define loop statement?

No, not in the way you think it is. What you can do instead is
something like this:

def do_something(i) :
... do_something ...

def loop(n, func):
for i in range(n): func(i)

loop(10, do_something)

Re: define loop statement?

David Isaac wrote:[color=blue]
> I would like to be able to define a loop statement
> (nevermind why) so that I can write something like
>
> loop 10:
> do_something
>
> instead of
>
> for i in range(10):
> do_something
>
> Possible? If so, how?[/color]

It's not possible to create a new statement, with suite
and indentation rules without hacking the interpreter or
resorting to alternative bytecode compilers such as "pyc".

Creating a _function_ named "loop" is easy as Jonathan's
answer shows.

Georg

Re: define loop statement?

David Isaac:[color=blue]
>I would like to be able to define a loop statement
>(nevermind why) so that I can write something like
>
>loop 10:
> do_something
>
>instead of
>
>for i in range(10):
> do_something
>
>Possible? If so, how?[/color]

Yes. By implementing a compiler or an interpreter for your programming
language. Or a preprocessor that converts your language to Python, or some
other suitable intermediate language. Or a programmer, that converts your
pseudocode and some coffee to the desired algorithm :-)

--
René Pijlman

Re: define loop statement?

David Isaac:[color=blue]
> I would like to be able to define a loop statement
> (nevermind why) so that I can write something like
>
> loop 10:
> do_something
>
> instead of
>
> for i in range(10):
> do_something
>
> Possible? If so, how?[/color]

It seems that you are looking for macros; maybe Logix "language"
(www.livelogix.net/logix) or Boo (boo.codehaus.o rg) can solve your
problem.
Otherwise you can do it with very different languages like Lisp or
Scheme (with a different syntax) and maybe Dylan too.

If you tell us your purpose, maybe we can suggest you a
better/different solution.

Bye,
bearophile

Re: define loop statement?

Rene Pijlman wrote:[color=blue]
> David Isaac:[color=green]
>> I would like to be able to define a loop statement
>> (nevermind why) so that I can write something like
>>
>> loop 10:
>> do_something
>>
>> instead of
>>
>> for i in range(10):
>> do_something
>>
>> Possible? If so, how?[/color]
>
> Yes. By implementing a compiler or an interpreter for your programming
> language. Or a preprocessor that converts your language to Python, or some
> other suitable intermediate language. Or a programmer, that converts your
> pseudocode and some coffee to the desired algorithm :-)
>[/color]
Or by hacking through the Python source and creating his own "somehow
pythonish but absolutely not python" language

Re: define loop statement?

Rene Pijlman wrote:[color=blue]
> David Isaac:[color=green]
>> I would like to be able to define a loop statement
>> (nevermind why) so that I can write something like
>>
>> loop 10:
>> do_something
>>
>> instead of
>>
>> for i in range(10):
>> do_something
>>
>> Possible? If so, how?[/color]
>
> Yes. By implementing a compiler or an interpreter for your programming
> language. Or a preprocessor that converts your language to Python, or some
> other suitable intermediate language. Or a programmer, that converts your
> pseudocode and some coffee to the desired algorithm :-)
>[/color]
Or by hacking through the Python source and creating his own "somehow
pythonish but absolutely not python" language

Re: define loop statement?

David Isaac wrote:[color=blue]
> I would like to be able to define a loop statement
> (nevermind why) so that I can write something like
>
> loop 10:
> do_something
>
> instead of
>
> for i in range(10):
> do_something
>
> Possible? If so, how?[/color]

Ruby and Smalltalk are both good at this kind of thing, since they have
syntactic support for associating a block with each method call. In
Python, I think you just have to do a little more setup. How about
something like this?

class Loop:
def __init__(self, n):
self.n = n
def __call__(self):
self.n = self.n - 1
return self.n != 0


if __name__ == '__main__':
loop = Loop(10)
while loop:
print "OK"

Re: define loop statement?

Jeffrey Schwab wrote:
[color=blue]
> class Loop:
> def __init__(self, n):
> self.n = n
> def __call__(self):
> self.n = self.n - 1
> return self.n != 0
>
>
> if __name__ == '__main__':
> loop = Loop(10)
> while loop:
> print "OK"[/color]

Seems you forgot "()" after "while loop" above.

Georg

Re: define loop statement?

Jeffrey Schwab wrote:
[color=blue]
> class Loop:
> def __init__(self, n):
> self.n = n
> def __call__(self):
> self.n = self.n - 1
> return self.n != 0
>
>
> if __name__ == '__main__':
> loop = Loop(10)
> while loop:[/color]

Whoops. Should be "while loop()".
[color=blue]
> print "OK"[/color]

Re: define loop statement?

[color=blue]
> Alan Isaac wrote:[color=green]
> > I would like to be able to define a loop statement
> > (nevermind why) so that I can write something like
> >
> > loop 10:
> > do_something
> >
> > instead of
> >
> > for i in range(10):
> > do_something
> >
> > Possible? If so, how?[/color][/color]


"Jeffrey Schwab" <jeff@schwabcen ter.com> wrote in message
news:T4LJf.1425 6$915.10437@sou theast.rr.com.. .[color=blue]
> class Loop:
> def __init__(self, n):
> self.n = n
> def __call__(self):
> self.n = self.n - 1
> return self.n != 0
>
>
> if __name__ == '__main__':
> loop = Loop(10)
> while loop():
> print "OK"[/color]

OK, that's pretty good.
Thanks!
Alan Isaac

Re: define loop statement?

Em Sáb, 2006-02-18 às 20:04 +0000, Jeffrey Schwab escreveu:[color=blue]
> if __name__ == '__main__':
> loop = Loop(10)
> while loop:
> print "OK"[/color]

Maybe:

while Loop(10)():
print "OK"

Looks rather ugly but requires one less line ;-).

--
"Quem excele em empregar a força militar subjulga os exércitos dos
outros povos sem travar batalha, toma cidades fortificadas dos outros
povos sem as atacar e destrói os estados dos outros povos sem lutas
prolongadas. Deve lutar sob o Céu com o propósito primordial da
'preservação' . Desse modo suas armas não se embotarão, e os ganhos
poderão ser preservados. Essa é a estratégia para planejar ofensivas."

-- Sun Tzu, em "A arte da guerra"

Re: define loop statement?

Felipe Almeida Lessa wrote:
[color=blue]
> Em Sáb, 2006-02-18 às 20:04 +0000, Jeffrey Schwab escreveu:[color=green]
>> if __name__ == '__main__':
>> loop = Loop(10)
>> while loop:
>> print "OK"[/color]
>
> Maybe:
>
> while Loop(10)():
> print "OK"
>
> Looks rather ugly but requires one less line ;-).
>[/color]
Doesn't work. You get a NEW Loop(10) instance on each pass through the
'while'. This is just an expensive way to make an endless loop.

--
Nigel Rowe
A pox upon the spammers that make me write my address like..
rho (snail) swiftdsl (stop) com (stop) au

Re: define loop statement?

Em Dom, 2006-02-19 às 11:08 +1100, Nigel Rowe escreveu:[color=blue]
> Felipe Almeida Lessa wrote:
>[color=green]
> > Em Sáb, 2006-02-18 às 20:04 +0000, Jeffrey Schwab escreveu:[color=darkred]
> >> if __name__ == '__main__':
> >> loop = Loop(10)
> >> while loop:
> >> print "OK"[/color]
> >
> > Maybe:
> >
> > while Loop(10)():
> > print "OK"
> >
> > Looks rather ugly but requires one less line ;-).
> >[/color]
> Doesn't work. You get a NEW Loop(10) instance on each pass through the
> 'while'. This is just an expensive way to make an endless loop.[/color]

Oh, sorry, ignore me on that one. Now I think I should sleep =S...

--
"Quem excele em empregar a força militar subjulga os exércitos dos
outros povos sem travar batalha, toma cidades fortificadas dos outros
povos sem as atacar e destrói os estados dos outros povos sem lutas
prolongadas. Deve lutar sob o Céu com o propósito primordial da
'preservação' . Desse modo suas armas não se embotarão, e os ganhos
poderão ser preservados. Essa é a estratégia para planejar ofensivas."

-- Sun Tzu, em "A arte da guerra"

Re: define loop statement?

David Isaac wrote:[color=blue]
> I would like to be able to define a loop statement
> (nevermind why) so that I can write something like
>
> loop 10:
> do_something[/color]

Here's a flagrant hack:

import sys

VAR_NAME = '__repeat_count er'

def set_repeat_coun ter(value):
frame = sys._getframe(2 )
frame.f_locals[VAR_NAME] = value

def get_repeat_coun ter(value):
frame = sys._getframe(2 )
if VAR_NAME not in frame.f_locals:
frame.f_locals[VAR_NAME] = value

return frame.f_locals[VAR_NAME]

def repeat(limit):
set_repeat_coun ter(get_repeat_ counter(limit)-1)
return get_repeat_coun ter(limit)

while repeat(10):
print 'OK'

Without more work it doesn't allow nested loops though.

And for the record, if you're worrying about Python's counted loop
construct you need better things to worry about.
<insert-smilies-as-appropriate>
--
Benji York