Take in the module OEIS the keyword 'dead' of sequences into account.

[PeterLuschny]

OEIS functions should simply ignore sequences with the
keyword 'dead'. At least they should not attempt to return
terms of these sequences.

For example the sequence A000017 https://oeis.org/A000017
is 'dead', what means it has errors in the data and was
replaced by another version. It is policy of the OEIS to
keep such sequences so they can be found in the case they
are referenced in the literature.

As it is now oeis(17).first_terms(12) throws the TypeError:
You found a sign inconsistency, please contact OEIS

CC: @mo271

Component: misc

Keywords: OEIS

Author: Moritz Firsching

Branch/Commit: d416ecc

Reviewer: Vincent Delecroix

Issue created by migration from https://trac.sagemath.org/ticket/17330

[mo271]

Commit: 8ea4b1a

[mo271]

Branch: u/moritz/ticket/17330

[mo271]

comment:1

Here is how this could be fixed (see git branch).

When doctesting this, I noticed the another bug:

**********************************************************************
File "src/sage/databases/oeis.py", line 845, in sage.databases.oeis.OEISSequence.keywords
Failed example:
    f.keywords()                          # optional -- internet
Expected:
    ('core', 'nonn', 'nice', 'easy', 'hear')
Got:
    ('core', 'nonn', 'nice', 'easy', 'hear', 'changed')
**********************************************************************

This is due to the fact that the keyword 'changed' is temporarily added, so this would go away after a while. I propose to change that example to a sequence that is not altered as often as the Fibonacci numbers (see commit)

---

New commits:

8ea4b1a

first try to fix 17330

[sagetrac-git]

Changed commit from 8ea4b1a to 10c15fc

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

10c15fc

second try to fix 17330

[videlec]

comment:5

You should put your full name in the "Authors" field.

[mo271]

Author: Moritz Firsching

[mo271]

comment:6

done

[videlec]

comment:7

The patch provided does not do what is in the description. Namely the dead sequences are not ignored!

I would add an explicit error message like

sage: oeis(17)
Traceback (most recent call last):
...
ValueError: this sequence is dead "A000017: Erroneous version of A032522."

Possibly, you could add an option to get it even if it is dead

sage: oeis(17, force=True)
A000017: Erroneous version of A032522.

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

d416ecc

adding a warning

[sagetrac-git]

Changed commit from 10c15fc to d416ecc

[videlec]

comment:9

Better!

[videlec]

Reviewer: Vincent Delecroix

[mo271]

Changed reviewer from Vincent Delecroix to none

[mo271]

comment:10

Perhaps throwing an error is too much? I just pushed a version where you have a warning..

[videlec]

Reviewer: Vincent Delecroix

[videlec]

comment:11

yeap. this is fine. (I rewrote my name as a reviewer)

[vbraun]

Changed branch from u/moritz/ticket/17330 to d416ecc