Re: [sage-combinat-devel] Re: Compositions in reverse order?
On Tue, Jan 22, 2013 at 04:33:33AM -0800, Nathann Cohen wrote: > Well, for a start you cannot ask Sage to reverse the iteration order of > anything that you can iterate on. > > First example : reversed(NN) > > And so there is no good solution in general unless you implement the > reversed iterator yourself, or list all elements. > > Then, instead of list(reversed(Compositions(4).list())) (which creates the > list twice in memory plus an interator on top of it), you can do this : > > C = Compositions(4).list() > C.reverse() > > Then : > for c in C: >print c > > or > > for i in range(len(C)): > print C[i] Tu peux faire aussi: sage: Compositions(4).list()[::-1] [[4], [3, 1], [2, 2], [2, 1, 1], [1, 3], [1, 2, 1], [1, 1, 2], [1, 1, 1, 1]] Par rapport à la solution de Nathann, je fais une copie... Florent -- You received this message because you are subscribed to the Google Groups "sage-combinat-devel" group. To post to this group, send email to sage-combinat-devel@googlegroups.com. To unsubscribe from this group, send email to sage-combinat-devel+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sage-combinat-devel?hl=en.
Re: [sage-combinat-devel] Re: Compositions in reverse order?
On Tue, Jan 22, 2013 at 04:33:33AM -0800, Nathann Cohen wrote: > > Well, for a start you cannot ask Sage to reverse the iteration order of > > anything that you can iterate on. > > > > First example : reversed(NN) > OK, but there is some inconsistent behavior, anyway: sage: P=Partitions(4) sage: len(P) 5 sage: C=Compositions(4) sage: len(C) --- AttributeErrorTraceback (most recent call last) /home/jyt/monge/TEX/QSCHUR/ in () /home/jyt/src/sage-5.4.1/local/lib/python2.7/site-packages/sage/combinat/combinat.py in __len__(self) 972 AttributeError: __len__ has been removed; use .cardinality() instead 973 """ --> 974 raise AttributeError, "__len__ has been removed; use .cardinality() instead" 975 976 def count(self): AttributeError: __len__ has been removed; use .cardinality() instead sage: R=reversed(P) sage: list(R) [[1, 1, 1, 1], [2, 1, 1], [2, 2], [3, 1], [4]] > > -- You received this message because you are subscribed to the Google Groups "sage-combinat-devel" group. To view this discussion on the web visit https://groups.google.com/d/msg/sage-combinat-devel/-/FOawuYfuDjwJ. To post to this group, send email to sage-combinat-devel@googlegroups.com. To unsubscribe from this group, send email to sage-combinat-devel+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sage-combinat-devel?hl=en.
Re: [sage-combinat-devel] Re: Compositions in reverse order?
Dear Jean-Yves, > OK, but there is some inconsistent behavior, anyway: > > > sage: P=Partitions(4) > sage: len(P) > 5 > sage: C=Compositions(4) > sage: len(C) > --- > AttributeErrorTraceback (most recent call last) > > /home/jyt/monge/TEX/QSCHUR/ in () > > /home/jyt/src/sage-5.4.1/local/lib/python2.7/site-packages/sage/combinat/combinat.py > > in __len__(self) > 972 AttributeError: __len__ has been removed; use > .cardinality() instead > 973 """ > --> 974 raise AttributeError, "__len__ has been removed; use > .cardinality() instead" > 975 > 976 def count(self): > > AttributeError: __len__ has been removed; use .cardinality() instead > sage: R=reversed(P) > sage: list(R) > [[1, 1, 1, 1], [2, 1, 1], [2, 2], [3, 1], [4]] Yes ! As you probably already guessed, everything is not yet in a clean state... The first call should raise the same error than the second one. We can't answer consistently to len because Python specified it as being a machine integer. This is much too small for cardinality of combinatorial set and prevent for returning infinity. So as the error message tell you, please write sage: P=Partitions(4) sage: P.cardinality() 5 sage: P=Partitions(4000) sage: P.cardinality() 1024150064776551375119256307915896842122498030313150910234889093895 sage: P=Partitions() sage: P.cardinality() +Infinity And indeed, I think that sage: len(Compositions(4000)) [...] AttributeError: __len__ has been removed; use .cardinality() instead Is a much clean behavior than: sage: len(Partitions(4000)) [...] RuntimeError: maximum recursion depth exceeded in cmp A++ Florent -- You received this message because you are subscribed to the Google Groups "sage-combinat-devel" group. To post to this group, send email to sage-combinat-devel@googlegroups.com. To unsubscribe from this group, send email to sage-combinat-devel+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sage-combinat-devel?hl=en.
Re: [sage-combinat-devel] Re: Compositions in reverse order?
> And indeed, I think that > > sage: len(Compositions(4000)) > [...] > AttributeError: __len__ has been removed; use .cardinality() instead > > Is a much clean behavior than: > > sage: len(Partitions(4000)) > [...] > RuntimeError: maximum recursion depth exceeded in cmp Then patch it, if it is a bug !!! O_O Nathann -- You received this message because you are subscribed to the Google Groups "sage-combinat-devel" group. To post to this group, send email to sage-combinat-devel@googlegroups.com. To unsubscribe from this group, send email to sage-combinat-devel+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sage-combinat-devel?hl=en.
Re: [sage-combinat-devel] Re: Compositions in reverse order?
On Wed, Jan 23, 2013 at 10:45:06AM +0100, Nathann Cohen wrote: > > And indeed, I think that > > > > sage: len(Compositions(4000)) > > [...] > > AttributeError: __len__ has been removed; use .cardinality() instead > > > > Is a much clean behavior than: > > > > sage: len(Partitions(4000)) > > [...] > > RuntimeError: maximum recursion depth exceeded in cmp > > Then patch it, if it is a bug !!! O_O Thanks for this very useful contribution ! Florent -- You received this message because you are subscribed to the Google Groups "sage-combinat-devel" group. To post to this group, send email to sage-combinat-devel@googlegroups.com. To unsubscribe from this group, send email to sage-combinat-devel+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sage-combinat-devel?hl=en.
Re: [sage-combinat-devel] Re: Compositions in reverse order?
> Thanks for this very useful contribution ! So what happens ? You know that there's a bug, it takes 3 seconds to fix it, and you don't ? Nathann -- You received this message because you are subscribed to the Google Groups "sage-combinat-devel" group. To post to this group, send email to sage-combinat-devel@googlegroups.com. To unsubscribe from this group, send email to sage-combinat-devel+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sage-combinat-devel?hl=en.
Re: [sage-combinat-devel] Re: Compositions in reverse order?
> > Yes ! As you probably already guessed, everything is not yet in a clean > state... The first call should raise the same error than the second one. > I understand, but in this case, one should teach "reversed" to use Cardinality instead of __len__. And this is python, not sage ... -- You received this message because you are subscribed to the Google Groups "sage-combinat-devel" group. To view this discussion on the web visit https://groups.google.com/d/msg/sage-combinat-devel/-/3XiisWOYN_gJ. To post to this group, send email to sage-combinat-devel@googlegroups.com. To unsubscribe from this group, send email to sage-combinat-devel+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sage-combinat-devel?hl=en.
Re: [sage-combinat-devel] Re: Compositions in reverse order?
Hey everyone, On Wednesday, January 23, 2013 3:42:55 AM UTC-8, Jean-Yves Thibon wrote: > > > >> Yes ! As you probably already guessed, everything is not yet in a clean >> state... The first call should raise the same error than the second one. >> > > I understand, but in this case, one should teach "reversed" to use > Cardinality instead of __len__. And this is python, not sage ... > > We could do this by just implementing the __reversed__() method in (the to be deprecated) CombinatorialClass. However on the deprecation note, we will need to decide whether or not __len__() and __reversed__() should be added to the (Finite) EnumeratedSets category. Without knowing exactly how sage handles __getitem__() with sage Integers passed in (my belief is everything is converted to machine ints and uses the python list (which is an array in memory [1]) ), I feel like we should leave __len__() alone since if we are trying to create/manipulate a list longer than int (and hence the machine) can handle, you need a better data structure and storage method and __len__() should fail in the same way as trying to create/retrieve the list. [1] http://stackoverflow.com/questions/914233/what-is-the-underlying-data-structure-for-python-lists Best, Travis -- You received this message because you are subscribed to the Google Groups "sage-combinat-devel" group. To view this discussion on the web visit https://groups.google.com/d/msg/sage-combinat-devel/-/rXatiGt2fAoJ. To post to this group, send email to sage-combinat-devel@googlegroups.com. To unsubscribe from this group, send email to sage-combinat-devel+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sage-combinat-devel?hl=en.
Re: [sage-combinat-devel] Re: Compositions in reverse order?
The problem is that, for the average user, Partitions(n), or
Compositions(n), or
Whatever(n) is expected to behave like, say, xrange(n). Removing __len__
breaks basic
python functionalities, results in head scratching ("What am I doing
wrong?"),
and drives the user to a hack-oriented programming style.
For algebraic purposes, I have never seen partitions of more than 25 or
compositions
of more than 16, let alone permutations of more than 14 .
For number theory or enumerative combinatorics, one needs much larger
values,
but a user trying to generate more than
2**62 = 4611686018427387904 objects will probably accept an overflow error.
So, why not let __len__ try to return int(cardinality) and throw and
exception if it is too large?
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Re: [sage-combinat-devel] Re: Compositions in reverse order?
Hi Jean-Yves,
I'm very happy to see you starting to use sage and giving us constructive
feedback.
On Wed, Jan 23, 2013 at 11:31:37PM -0800, Jean-Yves Thibon wrote:
>
> The problem is that, for the average user, Partitions(n), or
> Compositions(n), or
> Whatever(n) is expected to behave like, say, xrange(n). Removing __len__
> breaks basic
> python functionalities, results in head scratching ("What am I doing
> wrong?"),
> and drives the user to a hack-oriented programming style.
I'm not sure to agree with that. I also think, you are not an average Sage
user, you know way too much of Python. In this case "xrange(n)" is an
iterator, that is a Python/computer stuff, whereas Partitions(n) models the
sets of all partitions of n.
> For algebraic purposes, I have never seen partitions of more than 25 or
> compositions
> of more than 16, let alone permutations of more than 14 .
> For number theory or enumerative combinatorics, one needs much larger
> values,
> but a user trying to generate more than
> 2**62 = 4611686018427387904 objects will probably accept an overflow error.
>
> So, why not let __len__ try to return int(cardinality) and throw and
> exception if it is too large?
The main problem i see with that is that in many time cardinality is
implemented by running through the element... A similar problem is that I've
no way to prevent the user to write:
sage: list(Partitions())
...
infinite loop
which is closely related to
sage: len(Partitions())
...
AttributeError: __len__ has been removed; use .cardinality() instead
whereas I'd like to teach him as soon as possible to write
sage: Partitions().list()
[...]
NotImplementedError: infinite list
sage: Partitions().cardinality()
+Infinity
which both are fast to answer an perfectly makes sense. I've the feeling that
keeping the len stuff leads to more confusion for mathematician (not for
Python programmer).
Cheers,
Florent
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