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why no "do : until"?

Peter Hansen peter at engcorp.com
Sat Dec 30 21:12:13 EST 2000 
Steve Lamb wrote:
> 
> On Sat, 30 Dec 2000 23:00:53 GMT, Kragen Sitaker <kragen at dnaco.net> wrote:
> >Hahaha!  You just plonked Fredrik Lundh in comp.lang.python.  He was
> 
>     I can tell you I'll get far better without him than with him when he is
> giving advice that runs contrary to about 10+ years of programming that I've
> been taught from various different sources.  I don't care if he is God
> himself, advocating not initing a variable is stupid, plain and simple.  He
> wanted to argue the point for nothing more than argument's sake, so be it.  I
> don't need his advice any further.

It appears to me that you've missed some of the points made in this
"discussion".  I would suggest you go back with an open mind and
reconsider the validity of the opposing views.  The advice that runs
contrary to your 10+ years seems very reasonable to my 20+ years of
programming experience, and apparently many others with a variety of
experiences agree.  

I understand the point you are making; I'm just pointing out that the
opposing views seem well-founded.  Areas where I think you missed the
point are in the importance of code maintainability, the increased
complexity with your suggested approach, and the feelings of the "entire
CS community" on this issue.

If I may attempt to clarify what I believe is the opposing argument:  you
suggested an alternative which relies on initialization of a variable to a
special value (anything less than 25) solely in order to enter a 'while'
loop which you've rewritten to use the conditional at the top instead of
at the bottom (because you believe there is some inherent advantage in
doing this, though you've yet to explain what it is other than that the
use of 'break' is somehow bad), and in the process you've demonstrated the
*reason* others feel this is a poor approach, by leaving out the required
initialization.  And the first attempt to correct this was given using a
wrong value for the initializer!  That's the whole point: your approach is
inherently open to such complexity/maintainability problems.  Even
experienced programmers can slip up in this way.

I think those of us objecting have in our 10+ years of experience seen
this kind of thing cause so many problems that we are happy with the
single _idiomatic_ way which Python provides, in spite of a little
so-called "ugliness".  

I suspect some of us would even argue that the conditional in 'do/until'
can be difficult for some people to get right and that forcing the use of
'while/if/break' may actually increase the likelihood the resulting code
will be correct the first time, and be interpreted correctly during
maintenance.  My guess is that for this precise reason the alternative
loop construct was removed from/never added to Python in the first place.
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