add a method to reach lmfdb webpage of elliptic curves over Q

[fchapoton]

as suggested in #18968

CC: @JohnCremona @kedlaya @sagetrac-tmonteil

Component: elliptic curves

Author: Frédéric Chapoton

Branch/Commit: 2020242

Reviewer: John Cremona

Issue created by migration from https://trac.sagemath.org/ticket/21533

[fchapoton]

New commits:

d4781c3	trying to add links to lmfdb (not working)
8d7831e	Merge branch 'public/18968' in 7.4.b5
2020242	trac 18968 link to lmfdb page with correct url

[fchapoton]

Commit: 2020242

[fchapoton]

Branch: u/chapoton/21533

[fchapoton]

comment:3

any opinion on this proposal ?

[JohnCremona]

comment:4

Is there anywhere else in Sage where a function opens a web page ? Just wondering.

[fchapoton]

comment:5

There are already two instances:

git grep -P -c "webbrowser.open"
src/sage/databases/findstat.py:5
src/sage/databases/oeis.py:5

[fchapoton]

comment:6

ping ?

[JohnCremona]

comment:8

I will test this. It should be tested with and without the optional large database -- my own installations probably all have it so I hope someone else can test without.

[JohnCremona]

comment:9

I tested the branch after merging into current develop (7.6.beta0). It worked fine, starting a browser the first time and then opening new tabs in the same browser after that. If the curve is not in the database it gives a reasonable run-time error.

I'm sure that people will say that they should not have to install the optional database of curves if they can get the data from the LMFDB website; true (unless running Sage off-line) but work for the future.

Should we allow people to open the LMFDB URL of a valid elliptic curve label without constructin the curve? There could be a stand-alone function called (something like) open_lmfdb_elliptic_curve_page('label'), and then the elliptic curve method could call that.

Another follow-up would be for curves over number fields, which are currently being added to the database. But thelabelling is rather complicated to explain in this margin...

[fchapoton]

comment:10

I am not favourable to allow this call without building the curve.

[JohnCremona]

comment:11

That's OK. I'll just finish testing then and expect to give a +ve review soon.

[JohnCremona]

comment:12

When I remembered to doctest run the file with --optional=webbrowser,sage it worked fine (causing a page to pop up).

I did not test the part where an LMFDB label is used instead, since the curves obtained from the database do not have this field set. There's another ticket somewhere which will add these, and when that happens we'll see if that part of this code works as it should.

[JohnCremona]

Reviewer: John Cremona

[vbraun]

Changed branch from u/chapoton/21533 to 2020242