About generators

[Andrea Griffini]

On Mon, 26 Apr 2004 09:42:18 -0400, Peter Hansen <peter at engcorp.com>
wrote:

>Google Groups is always helpful for such questions:
>
>http://groups.google.com/groups?q=integer+range+syntax&meta=group%3Dcomp.lang.python.*
>
>This leads to various threads, such as the "Re: Thoughts on PEP284"
>which had the same proposal as yours and what is, I believe, an
>adequate reason for rejecting it.

Thanx for the pointer, but I wasn't able to find a discussion
about the use of a "normal" range binary operator; I found
things like

    for x in 0<= x < 10:
    for x in 10:
    for x in integers[0,1,...,10]:
    for x in integers[0:10]:

I personally find all those forms not better than (x)range; the
first one looks a test, not a definition of an iteration and in
math it doesn't imply any order, the others are at least as
obscure to me as (x)range.

Something that would be very similar to what is used in math
is probably

    for x in 1...10:

May be it's my math background, but I find things like

    squares = [x*x for x in 1...100]

quite readable

And yes, I also used to write a lot of Pascal code so the ".."
is more natural to me (I've also to confess that I use PERL,
even if this probably means I'll be mailbombed from readers
of this NG ;-) ).

But in math three are used, and the three-dot ellipsis is
already present in Python (even if I've still to understand
what's used for); so asking by using the three-dot one
seemed more correct to me.

To me it's very strange that the "range operator" approach
hasn't been discussed at least as much as those other (IMO)
much more exotic ones. Is this because it would be like
admitting that there is something good in PERL too ? :-DDD

Sure this would leave open a few problems, like how to specify
the step (how about the BASIC "step" ? it shouldn't create
any syntax ambiguity, I suppose) but those using increments
different from +1 are already less "natural", and a more
convolute syntax (range ?) or an explicit "while" could be
acceptable anyway; looping using +1 and accessing by "[-i]"
or "[i*3]" may be is more readable (and is used often in math).

Ok... too much talking for a newbie, I'm back to reading :-)

Andrea


PS: Oh, by the way. Very funny the idea of allowing ++x
    with the meaning it has in Python :-)