#20920: Changes to Unknown class
-------------------------------------+-------------------------------------
Reporter: eviatarbach | Owner:
Type: enhancement | Status: new
Priority: major | Milestone: sage-7.3
Component: misc | Resolution:
Keywords: days78 | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/eviatarbach/unknown | 7d95643efc6699998240ba08c95006ae4fd9c482
Dependencies: #20919 | Stopgaps:
-------------------------------------+-------------------------------------
Changes (by eviatarbach):
* dependencies: => #20919
* type: PLEASE CHANGE => enhancement
Old description:
> The `Unknown` class currently evaluates to `False` when converted to a
> boolean. This also leads to wrong results when using the logical
> operators, as explained in `unknown.py`.
>
> This ticket makes evaluating the truth value of `Unknown` with
> `__nonzero__` an error, meaning that logical operations must be done only
> with the bitwise operators. It also adapts the `UnknownClass` to add
> support for an `Undecidable` object, which is similar to `Unknown` but
> intended specifically for cases when an answer is known to be formally
> undecidable. This is useful for #17700.
New description:
The `Unknown` class currently evaluates to `False` when converted to a
boolean. This also leads to wrong results when using the logical
operators, as explained in `unknown.py`:
{{{
..warning:: Unless PEP 335 is accepted, in the following cases,
``and``, ``not`` and ``or`` return a somewhat wrong value::
sage: not Unknown # should return Unknown
True
}}}
This ticket makes evaluating the truth value of `Unknown` with
`__nonzero__` an error, meaning that logical operations must be done only
with the bitwise operators (since the logical operators cannot be
overridden). It also adapts the `UnknownClass` to add support for an
`Undecidable` object, which is similar to `Unknown` but intended
specifically for cases when an answer is known to be formally undecidable.
This is useful for #17700.
--
Comment:
Adding a preliminary patch. Some tests fail in `orthogonal_arrays.py` and
`difference_families.py` due to #20919.
--
Ticket URL: <https://trac.sagemath.org/ticket/20920#comment:2>
Sage <http://www.sagemath.org>
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