Re: iterators and views of lists

On Dec 20, 12:04 am, Anh Hai Trinh wrote: > chain: > >   sorted(itertools.chain(listagent(x)[::2], listagent(y)[-1:1:-2])) >   [0, 4, 8, 12, 13, 15, 16, 17, 19] > > zip: > >   sorted(itertools.izip(listagent(z)[1::3], listagent(x)[2::3])) >   [(452, 16), (758, 4), (898, 10)] I think I mis-interp

Re: iterators and views of lists

On Fri, 18 Dec 2009 21:10:28 -, Brendan Miller wrote: When I said they are "weak" I meant it in sense that the algorithms writeable against an InputerIterator interface (which is what python's iterator protocol provides) is a proper subset of the algorithms that can be written against a R

Re: iterators and views of lists

On Dec 18, 12:18 pm, "Alf P. Steinbach" wrote: [lots of tangential information snipped] > ...but I don't understand why you're limiting yourself to the STL. Because I believe the vast majority of iterators used in C++ in practice are the ones provided by STL types, therefore I felt a statement ab

Re: iterators and views of lists

On Dec 19, 5:47 am, Bearophile wrote: > It seems you have missed my post, so here it is, more explicitly: > > http://www.boostcon.com/site-media/var/sphene/sphwiki/attachment/2009... Interestingly, my `listagent` can be used as a lazy iterator and thus using itertools we can compose them just l

Re: iterators and views of lists

On 12/19/2009 12:10 AM, Gregory Ewing wrote: Terry Reedy wrote: On the other hand, Python indexes are a form of random access iterator, the top of the hierarchy. The term "random access iterator" seems oxymoronic to me. Iteration is all about operating on things in sequence. If you're accessin

Re: iterators and views of lists

On 12/17/2009 4:44 AM, Francesco Bochicchio wrote: On Dec 16, 1:58 pm, Anh Hai Trinh wrote: You might be interested in this library. You can easily create arbitrary "slice", for example i = mylist>> takei(primes()) will return an iterator over the i

Re: iterators and views of lists

On Fri, Dec 18, 2009 at 2:47 PM, Bearophile wrote: > Brendan Miller: >> I agree though, it doesn't matter to everyone and anyone. The reason I >> was interested was because i was trying to solve some specific >> problems in an elegant way. I was thinking it would be cool to make >> python more usa

Re: iterators and views of lists

Terry Reedy wrote: On the other hand, Python indexes are a form of random access iterator, the top of the hierarchy. The term "random access iterator" seems oxymoronic to me. Iteration is all about operating on things in sequence. If you're accessing elements arbitrarily, then you're not iterat

Re: iterators and views of lists

On Fri, 18 Dec 2009 10:39:15 -0800, Carl Banks wrote: > It is true that Python iterators can't be used to mutate the underlying > structure--if there is actual underlying data structure-- An iterator is a protocol. So long as you have __iter__ and next (or __next__ in Python 3) methods, your cl

Re: iterators and views of lists

Brendan Miller: > I agree though, it doesn't matter to everyone and anyone. The reason I > was interested was because i was trying to solve some specific > problems in an elegant way. I was thinking it would be cool to make > python more usable in programming competitions by giving it its own > por

Re: iterators and views of lists

On 12/18/2009 1:00 AM, Brendan Miller wrote: For the benefit of those of us who aren't C++ programmers, what do its iterators do that Python's don't? It depends on what one means by 'iterator'. Python iterators do not fit in the STL hierarchy. On the other hand, Python indexes are a form of

Re: iterators and views of lists

On Fri, Dec 18, 2009 at 10:39 AM, Carl Banks wrote: > On Dec 17, 10:00 pm, Brendan Miller wrote: >> On Thu, Dec 17, 2009 at 6:44 PM, Steven D'Aprano >> >> 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

Re: iterators and views of lists

* Carl Banks: On Dec 18, 11:08 am, "Alf P. Steinbach" wrote: * Carl Banks: On Dec 17, 10:00 pm, Brendan Miller wrote: On Thu, Dec 17, 2009 at 6:44 PM, Steven D'Aprano wrote: On Thu, 17 Dec 2009 12:07:59 -0800, Brendan Miller wrote: I was thinking it would be cool to make python more us

Re: iterators and views of lists

On Dec 18, 11:08 am, "Alf P. Steinbach" wrote: > * Carl Banks: > > > > > On Dec 17, 10:00 pm, Brendan Miller wrote: > >> On Thu, Dec 17, 2009 at 6:44 PM, Steven D'Aprano > > >> wrote: > >>> On Thu, 17 Dec 2009 12:07:59 -0800, Brendan Miller wrote: > I was thinking it would be cool to make p

Re: iterators and views of lists

On 12/18/2009 7:07 AM, Brendan Miller wrote: As for copying pointers not taking much time... that depends on how long the list is. if you are working with small sets of data, you can do almost anything and it will be efficient. However, if you have megabytes or gigabytes of data (say you are work

Re: iterators and views of lists

* Carl Banks: On Dec 17, 10:00 pm, Brendan Miller wrote: On Thu, Dec 17, 2009 at 6:44 PM, Steven D'Aprano 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

Re: iterators and views of lists

On Dec 17, 10:00 pm, Brendan Miller wrote: > On Thu, Dec 17, 2009 at 6:44 PM, Steven D'Aprano > > 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 th

Re: iterators and views of lists

On Dec 18, 3:07 am, Brendan Miller wrote: > Well, it doesn't really need to be any slower than a normal list. You > only need to use index and do extra additions because it's in python. > However, if listagent were written in C, you would just have a pointer > into the contents of the original li

Re: iterators and views of lists

On Thu, Dec 17, 2009 at 6:44 PM, Steven D'Aprano 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 alon

Re: iterators and views of lists

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 benefi

Re: iterators and views of lists

On Thu, Dec 17, 2009 at 8:41 AM, Anh Hai Trinh wrote: >> I have a couple of thoughts: >> 1. Since [:] by convention already creates a copy, it might violate >> people's expectations if that syntax were used. > > Indeed, listagent returns self on __getitem__[:]. What I meant was > this: > >  x = [0

Re: iterators and views of lists

> I have a couple of thoughts: > 1. Since [:] by convention already creates a copy, it might violate > people's expectations if that syntax were used. Indeed, listagent returns self on __getitem__[:]. What I meant was this: x = [0, 1, 2, 3, 4, 5, 6, 7] a = listagent(x)[::2] a[:] = listagent

Re: iterators and views of lists

On Wed, Dec 16, 2009 at 12:38 PM, Anh Hai Trinh wrote: > On Dec 16, 2:48 pm, Brendan Miller wrote: > >> No, that's what I'm getting at... Most of the existing mutating >> algorithms in python (sort, reverse) operate over entire collections, >> not partial collections delimited by indexes... which

Re: iterators and views of lists

On Dec 16, 2:48 pm, Brendan Miller wrote: > No, that's what I'm getting at... Most of the existing mutating > algorithms in python (sort, reverse) operate over entire collections, > not partial collections delimited by indexes... which would be really > awkward anyway. Ok it can be done! The cod

Re: iterators and views of lists

On Wed, Dec 16, 2009 at 4:16 AM, Paul Rudin wrote: > Steven D'Aprano writes: > > >> I'm sympathetic to your request for list views. I've often wanted some >> way to cleanly and neatly do this: >> >> for item in seq[1:]: >>     process(item) >> >> without making an unnecessary copy of almost all o

Re: iterators and views of lists

On Dec 16, 1:58 pm, Anh Hai Trinh wrote: > > You might be interested in this library stream>. > > You can easily create arbitrary "slice", for example > >   i = mylist >> takei(primes()) > > will return an iterator over the items of mylist with a prime number > ind

Re: iterators and views of lists

On Wed, Dec 16, 2009 at 5:39 AM, Steven D'Aprano < st...@remove-this-cybersource.com.au> wrote: > for item in seq[1:]: >process(item) > > without making an unnecessary copy of almost all of seq. > I use the following idiom: for i in range(1, len(seq)): process(seq[i]) Alternately, if I'm

Re: iterators and views of lists

On Wed, Dec 16, 2009 at 7:33 AM, Peter Otten <__pete...@web.de> wrote: > islice() could be changed to special-case lists and tuples, but that feels > a > bit unclean. > How about special-casing objects that implement collections.Sequence? -- Daniel Stutzbach, Ph.D. President, Stutzbach Enterpris

Re: iterators and views of lists

On Dec 15, 11:48 pm, Brendan Miller wrote: > I was thinking you'd want something like random access iterators in > c++, or pointers in c, to write typical in place algorithmic code. To > me, something like non-copying slices (maybe you'd call it a list > view?) would seem functionally similar and

Re: iterators and views of lists

Paul Rudin wrote: > Steven D'Aprano writes: > > >> I'm sympathetic to your request for list views. I've often wanted some >> way to cleanly and neatly do this: >> >> for item in seq[1:]: >> process(item) >> >> without making an unnecessary copy of almost all of seq. >> > > I don't know how

Re: iterators and views of lists

On Dec 16, 10:39 am, Brendan Miller wrote: > I was trying to reimplement some of the c++ library of generic > algorithms in c++ in python, but I was finding that this is > problematic to do this in a generic way because there isn't any > equivalent of c++'s forward iterators, random access iterato

Re: iterators and views of lists

Steven D'Aprano writes: > I'm sympathetic to your request for list views. I've often wanted some > way to cleanly and neatly do this: > > for item in seq[1:]: > process(item) > > without making an unnecessary copy of almost all of seq. > I don't know how it's implemented - but presumably i

Re: iterators and views of lists

On Tue, 15 Dec 2009 23:48:04 -0800, Brendan Miller wrote: > On Tue, Dec 15, 2009 at 9:09 PM, Terry Reedy wrote: >> On 12/15/2009 10:39 PM, Brendan Miller wrote: >>> I'm wondering if anyone has done work towards creating more powerful >>> iterators for python, or creating some more pythonic equiva

Re: iterators and views of lists

Brendan Miller: > Currently people slice and dice with well... slices, but those are > copying, so if you want to operate over part of a range you make a > copy, perform the operation, then copy the results back in. > > I was thinking you'd want something like random access iterators in > c++, or p

Re: iterators and views of lists

On Tue, Dec 15, 2009 at 9:09 PM, Terry Reedy wrote: > On 12/15/2009 10:39 PM, Brendan Miller wrote: >> I'm wondering if anyone has done work towards creating more powerful >> iterators for python, or creating some more pythonic equivalent. > > For sequences, integer indexes let you do anything you

Re: iterators and views of lists

On 12/15/2009 10:39 PM, Brendan Miller wrote: I was trying to reimplement some of the c++ library of generic algorithms in c++ in python, but I was finding that this is problematic to do this in a generic way because there isn't any equivalent of c++'s forward iterators, random access iterators,

iterators and views of lists

I was trying to reimplement some of the c++ library of generic algorithms in c++ in python, but I was finding that this is problematic to do this in a generic way because there isn't any equivalent of c++'s forward iterators, random access iterators, etc. i.e. all python iterators are just input it