Replace is_Set() usage

[rwst]

Replace calls to is_Set with the code it has, which is just isinstance(x, Set_generic).

Component: basic arithmetic

Author: Ralf Stephan

Branch/Commit: 6972d8d

Reviewer: Vincent Delecroix

Issue created by migration from https://trac.sagemath.org/ticket/24443

[rwst]

Branch: u/rws/make_realset_answer_positive_to_is_set

[rwst]

New commits:

706c762

24443: Make RealSet answer positive to is_Set

[rwst]

Author: Ralf Stephan

[rwst]

Commit: 706c762

[videlec]

comment:3

is_Set is not intended to answer the question "is this object a set". There is no need to let RealSet inherits from Set_generic. As I already mentioned in #15344, what does work is

sage: RealSet(1,2) in Sets()
True

[rwst]

comment:4

In that case I'd like to either rename is_Set or replace calls to it with the code it has, which is just isinstance(x, Set_generic). Outside of sage/sets grep finds the following usages of which I'm not sure if they are even correct:

src/sage/combinat/set_partition.py:from sage.sets.set import Set, is_Set
src/sage/combinat/set_partition.py:        if not (isinstance(x, (SetPartition, set, frozenset)) or is_Set(x)):
src/sage/combinat/set_partition.py:            if not (isinstance(s, (set, frozenset)) or is_Set(s)):
src/sage/combinat/set_partition_ordered.py:from sage.sets.set import Set, is_Set
src/sage/combinat/set_partition_ordered.py:            if not isinstance(s, (set, frozenset)) and not is_Set(s):
src/sage/combinat/partition_algebra.py:from sage.sets.set import Set, is_Set
src/sage/combinat/partition_algebra.py:            assert isinstance(s, (set, frozenset)) or is_Set(s)

What do you think?

[mantepse]

comment:5

At least from what I understand, these calls to is_Set are correct, and I agree that

isinstance(x, (SetPartition, set, frozenset, Set_generic))

would be easier to understand for me.

More precisely: I believe that this code is to make

sage: Set([Set([1,2])]) in SetPartitions
True

work.

[videlec]

comment:6

Replying to @rwst:

In that case I'd like to either rename is_Set or replace calls to it with the code it has, which is just isinstance(x, Set_generic). Outside of sage/sets grep finds the following usages of which I'm not sure if they are even correct:

src/sage/combinat/set_partition.py:from sage.sets.set import Set, is_Set
src/sage/combinat/set_partition.py:        if not (isinstance(x, (SetPartition, set, frozenset)) or is_Set(x)):
src/sage/combinat/set_partition.py:            if not (isinstance(s, (set, frozenset)) or is_Set(s)):
src/sage/combinat/set_partition_ordered.py:from sage.sets.set import Set, is_Set
src/sage/combinat/set_partition_ordered.py:            if not isinstance(s, (set, frozenset)) and not is_Set(s):
src/sage/combinat/partition_algebra.py:from sage.sets.set import Set, is_Set
src/sage/combinat/partition_algebra.py:            assert isinstance(s, (set, frozenset)) or is_Set(s)

What do you think?

It has started long ago

• sage.schemes.projective.projective_space.is_ProjectiveSpace
• sage.schemes.product_projective.space.is_ProductProjectiveSpaces
• sage.rings.polynomial.polynomial_ring.is_PolynomialRing
• sage.rings.ring.is_Ring
• etc

The only reasonable solution is to agree with all other developers (on sage-devel) that we want to remove them all from Sage (I am +1 for it). Then we could start with a "task ticket" listing all the is_X and start concretely by removing is_Set.