EmptySet is Back ! TestSuite should allows for empty sets.

[hivert]

There is currently no way to have an empty set which pass the category tests. Indeed the current specification says: for any set S there must be a method S.an_element() which returns an actual element x such that x in S:

an_element = self.an_element()
tester.assert_(an_element in self, "self.an_element() is not in self")

This tests should allows S to be empty.

To solve this issue I added a new exception called EmptySetError which should be raised in such cases. I fixed the tests suite of the category Sets() accordingly and expanded the test in some places where this could be done before.

Depends on #8519

CC: @sagetrac-nborie @sagetrac-sage-combinat

Component: categories

Keywords: empty set, Testsuite, EmptySetError

Author: Florent Hivert

Reviewer: Nicolas Borie, Nicolas M. Thiéry

Merged: sage-4.4.alpha0

Issue created by migration from https://trac.sagemath.org/ticket/8543

[hivert]

Attachment: trac_8543-empty_set_categories-fh.patch.gz

[hivert]

Changed keywords from empty set, Testsuite to empty set, Testsuite, EmptySetError

[sagetrac-nborie]

comment:2

Patches from #8519 your patch apply fine on 4.3.4
All tests passed for each touched files, doc is OK too. This another empty problem is fixed...

Thanks for fixing this!

I give this patch a positive review...

[sagetrac-nborie]

Reviewer: Nicolas Borie

[nthiery]

comment:3

Nicolas: thanks for your review!

Florent: I made a quick reviewer patch fixing some trivial things. Please double check, and set back the positive review!

[nthiery]

comment:4

Attachment: trac_8543-empty_set_categories-review-nt.patch.gz

[nthiery]

Changed reviewer from Nicolas Borie to Nicolas Borie, Nicolas M. Thiéry

[hivert]

comment:7

The new changes are good to me => positive review.

[jhpalmieri]

Merged: sage-4.4.alpha0

[jhpalmieri]

comment:8

Merged in 4.4.alpha0:

• trac_8543-empty_set_categories-fh.patch
• trac_8543-empty_set_categories-review-nt.patch