update docstrings for chart saving

[RossKen]

Type of PR

• BUG
• FEAT
• MAINT
• DOC

Is your Pull Request linked to an existing Issue or Pull Request?

Closes #1441

Give a brief description for the solution you have provided

Update chart saving examples in chart docstrings

PR Checklist

• Added documentation for changes
• Added feature to example notebooks at tutorial in splink_demos (if appropriate)
• Made changes based off the latest version of Splink
• Run the linter

[github-actions]

Test: test_2_rounds_1k_duckdb

Percentage change: -11.4%

	date	time	stats_mean	stats_min	commit_info_branch	commit_info_id	machine_info_cpu_brand_raw	machine_info_cpu_hz_actual_friendly	commit_hash
849	2022-07-12	18:40:05	1.89098	1.87463	splink3	c334bb9	Intel(R) Xeon(R) Platinum 8370C CPU @ 2.80GHz	2.7934 GHz	c334bb9
1866	2023-07-18	13:46:20	1.67135	1.6603	(detached head)	9d59e56	Intel(R) Xeon(R) Platinum 8171M CPU @ 2.60GHz	2.0951 GHz	9d59e56

Test: test_2_rounds_1k_sqlite

Percentage change: -1.0%

	date	time	stats_mean	stats_min	commit_info_branch	commit_info_id	machine_info_cpu_brand_raw	machine_info_cpu_hz_actual_friendly	commit_hash
851	2022-07-12	18:40:05	4.32179	4.25898	splink3	c334bb9	Intel(R) Xeon(R) Platinum 8370C CPU @ 2.80GHz	2.7934 GHz	c334bb9
1868	2023-07-18	13:46:20	4.2601	4.21841	(detached head)	9d59e56	Intel(R) Xeon(R) Platinum 8171M CPU @ 2.60GHz	2.0951 GHz	9d59e56

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[NickCrews]

Looks great to me @RossKen !

[RobinL]

Whilst this looks like the best option, unfortunately it's not possible to do it this way.

The reason is that chart.save(.html) produces (I believe , but worth checking) a chart which works as a standalone web page only if you have an internet connection, whilst this function seeks to allow users in airgapped environments to use the chart.

So it needs to follow a similar approach as before, but now retrieve the chart spec from the altair chart (sorry can't remember the method for that and am on my phone)

I'm not actually sure how this interacts with the .PNG saving. I guess that probably does work offline, so the need for this function is somewhat lower, but you'd probably loose the tooltip and any other interactivity

[NickCrews]

Ahhh, yes that makes sense. Darn.

It looks like https://github.com/altair-viz/altair_saver solves this with save(chart, "chart.html", inline=True) # HTML document with all JS code included inline?

[RobinL]

Ahhh, yes that makes sense. Darn.

It looks like https://github.com/altair-viz/altair_saver solves this with save(chart, "chart.html", inline=True) # HTML document with all JS code included inline?

Good spot! - I was not aware of that. So comes down to whether we want the additional dependency. Since we already have working code, and Splink gets installed on quite a lot of strange infrastructure (often airgapped, with limited access to pypi) I'd probably err on the side of not adding the dependency, but I don't have particularly strong views

[RossKen]

Given we probably don't want to add more dependencies, should we close this PR?

[RobinL]

There's still a bug, it's just that now the charts are altair.Charts, to retrieve the chart as a dict you need chart.to_dict() see here rather than chart.spec

[ThomasHepworth]

I shall rescind my approval upon reading Robin's review...

[ThomasHepworth]

Once addressed, I'll approve
#1450 (comment)

[RobinL]

This is already fixed by https://github.com/moj-analytical-services/splink/pull/1694/files