[Python-Dev] Visibility scope for "for/while/if" statements

Josiah Carlson jcarlson at uci.edu
Thu Sep 22 21:00:51 CEST 2005

Alexander Myodov <maa_public at sinn.ru> wrote:
[snip Alexander Myodov complaining about how Python works]

> i = 0
> while i != 1:
>     i += 1
>     j = 5
> print j

Maybe you don't realize this, but C's while also 'leaks' internal

int i = 0, j;
while (i != 1) {
    j = 5;
printf("%i %i\n", i, j);

If you haven't yet found a good use for such 'leakage', you should spend
more time programming and less time talking; you would find (quite
readily) that such 'leaking' is quite beneficial.

> I made several loops, one by one, using the "i" variable for looping.
> Then in the latest loop I changed the "i" name to more meaningful
> "imsi" name in the "for" declaration and whenever I found inside the loop.
> As I use "i" name *for loops exclusively*, I didn't wittingly reuse the
> same name for different purposes. The problem was that I missed one
> occurance of "i" variable inside the loop code, so it gained the same
> value (from the completion of previous loop) throughout all the "imsi"
> loop. And the interpreter didn't notice me that "I am using the
> undefined variable" (since it is considered defined in Python), as
> accustomed from other languages. That's my sorrowful story.

So you mistyped something.  I'm crying for you, really I am.

> But for the "performance-oriented/human-friendliness" factor, Python
> is anyway not a rival to C and similar lowlevellers. C has
> pseudo-namespaces, though.

C does not have pseudo-namespaces or variable encapsulation in for loops.

Ah hah hah!  Look ladies and gentlemen, I caught myself a troll!  Python
does not rival C in the performance/friendliness realm?  Who are you
trying to kid?  There is a reason why high school teachers are teaching
kids Python instead of Pascal, Java, etc., it's because it is easier to
learn and use.  On the performance realm, of course Python is beat out
by low-level languages; it was never meant to compete with them.  Python
does what it can for speed when such speed does not affect the usability
of the language.  What you are proposing both would reduce speed and
usability, which suggests that it wasn't a good idea in the first place.

> JC> Python semantics seem to have been following the rule of "we are all
> JC> adults here".
> I always believed that the programming language (as any computer
> program) should slave to the human, rather than a human should slave
> to the program.

Your beliefs were unfounded.  If you look at every programming language,
there are specific semantics and syntax for all of them.  If you fail to
use and/or understand them, the langauge will not be your 'slave'; it
will not run correctly, if at all.

> "for (int i = 0; i < 10; i++)" works fine nowadays.

I'm sorry, but you are wrong.  The C99 spec states that you must define
the type of i before using it in the loop.  Maybe you are thinking of
C++, which allows such things.

> JC> Also: python-dev is a mailing list for the development /of/ Python.
> JC> Being that your questions as of late have been in the realm of "why does
> JC> or doesn't Python do this?", you should go to python-list (or the
> JC> equivalent comp.lang.python newsgroup) for answers to questions
> JC> regarding current Python behavior, and why Python did or didn't do
> JC> something in its past.
> I'm sorry for wasting the time of developers. For "for/while/if"
> statements, I just had an idea which (I believed) could be useful for
> many peoples,

Test your ideas on comp.lang.python first, when more than a handful of
people agree with you, come back.

 - Josiah

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