#13747: Change default behaviour of Poset to facade = True
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Reporter: ncohen | Owner: sage-combinat
Type: defect | Status: new
Priority: major | Milestone: sage-5.6
Component: combinatorics | Keywords:
Work issues: | Report Upstream: N/A
Reviewers: | Authors: Nathann Cohen
Merged in: | Dependencies:
Stopgaps: |
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As mentionned in the following discussions :
* http://groups.google.com/forum/#!msg/sage-devel/qQzzZEh-JRo/WxU_qyxH2igJ
* http://groups.google.com/d/topic/sage-combinat-
devel/bfWbG54sedM/discussion (sage-combinat fork of the discussion)
* https://groups.google.com/d/topic/sage-devel/xQxQLkm-RUU/discussion
This patch changes the default behaviour of the Poset constructor to
facade = True, so that the elements that you define the Poset with are the
elements it contains.
Two comments about this ticket :
* While the documentation of the poset/ files say that `facade` is a
boolean, it is not. Its former default value is actually `None`, and the
code itself tests several times `if facade is None`. No idea why. All I
know is that I first tried to make it really boolean, and to replace those
`None` tests by `if not facade`, but I was not able to make all tests pass
without any idea why. I added a warning about this in the file's header,
and the doctests based on the former versions of Posets are now defined
with a `facade = None` flag. Even though it should be a boolean. Well, if
this wasn't a problem before, no reason why it should become one now. This
clearly has to be fixed too.
* There is a `Poset.linear_extensions` method whose default behaviour is
also `facade = None`. Despite taking an optional flag, this method *DOES
NOT WORK* as it is clearly indicated in its docstring. One can easily
wonder what the hell this function is doing in Sage's code. Hence this
function's behaviour is left untouched. It will use `facade=None` by
default until it is rewritten correctly, or removed.
Nathann
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13747>
Sage <http://www.sagemath.org>
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