* Carl Banks:
On Dec 18, 11:08 am, "Alf P. Steinbach" <al...@start.no> wrote:
* Carl Banks:
On Dec 17, 10:00 pm, Brendan Miller <catph...@catphive.net> wrote:
On Thu, Dec 17, 2009 at 6:44 PM, Steven D'Aprano
<st...@remove-this-cybersource.com.au> wrote:
On Thu, 17 Dec 2009 12:07:59 -0800, Brendan Miller wrote:
I was thinking it would be cool to make python more usable in
programming competitions by giving it its own port of the STL's
algorithm library, which needs something along the lines of C++'s more
powerful iterators.
For the benefit of those of us who aren't C++ programmers, what do its
iterators do that Python's don't?
Python iterators basically only have one operation:
next(), which returns the next element or throws StopIteration.
In C++ terminology this is a Input iterator. It is good for writing
"for each" loops or map reduce operations.
Hmm. I guess the main thing that's bothering me about this whole
thread is that the true power of Python iterators is being overlooked
here, and I don't think you're being fair to call Python iterators
"weak" (as you did in another thread) or say that they are only good
for for-else type loops.
The fact is, Python iterators have a whole range of powers that C++
iterators do not. C++ iterators, at least the ones that come in STL,
are limited to iterating over pre-existing data structures. Python
iterators don't have this limation--the data being "iterated" over can
be virtual data like an infinite list, or data generated on the fly.
This can be very powerful.
It's good that Python iterators can do things.
However, it's not the case that C++ iterators can't do those things.
C++ iterators very much routinely do such things.
STL Iterators? No. Maybe if you're talking about boost or homemade
iterators or something I could buy it, though I'd still bs suspicious
of "routinely".
The intersection of STL and the C++ standard library is of nearly the same size
as the STL, but I don't understand why you're limiting yourself to the STL.
After all, the STL was first developed for the Ada language, IIRC.
Using the standard C++ library, per the 1998 first (and current!) C++ standard,
below is an idiomatic "copy Carl Banks to output" C++ program where, you might
note, the "ostream_iterator" has a sister "istream_iterator" that definitely
does not only iterat over a "pre-existing data structure", as you wrote.
Of course, mostly one defines iterators in the source code or by using Boost or
similar libraries; that's how C++ works.
There's no special language support for iterators in C++; it's wholly a library
and application defined concept.
<code>
#include <iostream>
#include <iterator>
#include <vector>
#include <algorithm>
int main()
{
using namespace std;
static char const* const words[] =
{ "Carl", "Banks", "is", "wrong", "on", "the", "Internet", "!" };
copy(
words, words + sizeof(words)/sizeof(*words),
ostream_iterator<char const*>( cout, "\n" )
);
}
</code>
Cheers & hth.,
- Alf
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