Python IF THEN chain equivalence

[jzakiya]

On Nov 13, 5:48 pm, "M.-A. Lemburg" <m... at egenix.com> wrote:
> On 2008-11-13 23:31, jzakiya wrote:
>
>
>
> > On Nov 13, 5:21 pm, Alan Baljeu <alanbal... at yahoo.com> wrote:
> >> I think you should rethink your post. The first case you posted makes no sense in any language I know.  Also, a whole lot of nested IF's is a bad idea in any language.  In Python, you will end up with code indented 40+ characters if you keep going.
>
> >> ----- Original Message ----
> >> From: jzakiya <jzak... at mail.com>
> >> To: python-l... at python.org
> >> Sent: Thursday, November 13, 2008 5:06:53 PM
> >> Subject: Python IF THEN chain equivalence
>
> >> I'm translating a program in Python that has this IF Then chain
>
> >> IF  x1 < limit:   --- do a ---
> >>     IF  x2 < limit:  --- do b ---
> >>         IF x3 < limit:  --- do c ---
> >>                        .-----
> >>                         ------
> >>                     IF  x10 < limt: --- do j ---
> >>                     THEN
> >>                  THEN
> >>               -----
> >>           THEN
> >>      THEN
> >> THEN
>
> >> In other words, as long as    'xi' is less than 'limit' keep going
> >> down the chain, and when 'xi' isn't less than 'limit' jump to end of
> >> chain a continue.
>
> >> Is this the equivalence in Python?
>
> >> IF  x1 < limit:
> >>         --- do a  ---
> >> elif x2 < limit:
> >>         --- do b ---
> >> ----
> >> ----
> >> elif x10 < limit:
> >>        --- do j ---
>
> >> --http://mail.python.org/mailman/listinfo/python-list
>
> >>       __________________________________________________________________
> >> Ask a question on any topic and get answers from real people. Go to Yahoo! Answers and share what you know athttp://ca.answers.yahoo.com
>
> > In the code the 'xi's and 'limit' are variables and the --- do letters
> > ---
> > phrases are simply writes to any array:   an_array[xi]=0
>
> > Actually, the code makes perfectly good sense, and is a necessity of
> > the algorithm I'm implementing, and works perfectly good in Forth, and
> > can be
> > written quite nicely within a normal page width.
>
> > I was just hoping I could perform the equivalent chain in Python
> > without
> > having to grossly indent the source code past the normal width of a
> > printed page.
> > But if that's the only way to do it in Python, then so be it.
>
> You should probably consider using a function and then
> convert the conditions to define return points:
>
> def do_something(...args...):
>
>     if x1 >= limit:
>         return
>     ...do a...
>     if x2 >= limit:
>         return
>     ...do b...
>     etc.
>
> That is provided I understand the flow of control in your
> example... it's kind of strange to have THEN mark the *end*
> of the then-branch in an if-then-else construct.
>
> --
> Marc-Andre Lemburg
> eGenix.com
>
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It's interesting to see people think it's strange to have code that
has multiple nested levels of IF THEN.  Apparently you haven't seen
any Forth, assembly, et al code. All you're doing is having the branch
point for each conditional be the end of the chain, otherwise it falls
through to the code after the conditional.  This is done all the time
in languages that let you actually manipulate the hardware.

Just as a suggestion :-)  a little humility would go a long way toward
being open minded and receptive to different paradigms.  I've written
this program I'm doing now in Python in 3 other languages (including
Python, which I'm trying to make more efficient) and I seek to be
flexible in my software linguistic capabilities.

I asked a very narrow question about a very specific language
mechanism, and I know exactly what and why I'm doing what I'm doing.

I'll try some of the suggestions and see if they make the routine
faster in Python.