Splink Altair graph saving

[illeamb]

I have been using the SPLINK package recently.

I was wondering how I can save some of the graphs that are generated from Splink. So the object that I am trying to print are :

linker.match_weights_chart()
linker.m_u_parameters_chart()

They appear to be Vegalite objects. Is there an easy way to save them as a png file? I wasn't sure whether there was any documentation on how to save the objects. If I have missed it, feel free to point me in the right direction.

Edit and Solution from maintainers 2023-06-16
This question is now out of date due to this PR

All charts produced Splink are now full Altair Charts alt.Chart(). You need to have Altair version 5 for them to work.

This means all charts can now be more easily saved using e.g. chart.save("myfile.png"). Note you can use file extensions json, png, svg, pdf, or html and others depending on what type output you want

Since all charts are now proper Altair charts, users experiencing difficulties should be asked to look at the Altair documentation.

[illeamb]

So further to that I had a look through the splink source code and managed to save the objects as html file with the sample code below:

from splink import charts
plot_obj=restrictive_linker.m_u_parameters_chart()
charts.save_offline_chart(plot_obj,filename="test.html",overwrite=True)

I can see the charts in html format on the browser. How do I convert it to png through python?

[RobinL]

Sorry - this is a little more trouble than it should be due to us using some of the newest vega lite features that haven't yet made it into Altair on pypi

I think you need to install (see also the 'additional requirements')
https://github.com/altair-viz/altair_saver/

And then

import altair_saver
c = linker.match_weights_chart()
altair_saver.save(c.spec, "saved.png")

Alternatively you could use the CLI described here:
https://vega.github.io/vega/usage/#:~:text=Back%20to%20reference-,Command%20Line%20Utilities,-The%20vega%2Dcli

to render the c.spec dictionary by calling out to the command line

[illeamb]

Yeah, so tried something similar earlier and now tried your code snippet. I get the following error on both. I am using altair_saver version '0.5.0'.

---

ValueError Traceback (most recent call last)
Cell In [12], line 3
1 import altair_saver
2 c = linker.match_weights_chart()
----> 3 altair_saver.save(c.spec, "saved.png")

File /usr/local/lib/python3.9/site-packages/altair_saver/_core.py:169, in save(chart, fp, fmt, mode, embed_options, method, suppress_data_warning, **kwargs)
166 if embed_options is None:
167 embed_options = alt.renderers.options.get("embed_options", None)
--> 169 Saver = _select_saver(method, mode=mode, fmt=fmt, fp=fp)
170 saver = Saver(spec, mode=mode, embed_options=embed_options, **kwargs)
172 return saver.save(fp=fp, fmt=fmt)

File /usr/local/lib/python3.9/site-packages/altair_saver/_core.py:69, in _select_saver(method, mode, fmt, fp)
67 if s.enabled() and fmt in s.valid_formats[mode]:
68 return s
---> 69 raise ValueError(f"No enabled saver found that supports format={fmt!r}")
70 else:
71 raise ValueError(f"Unrecognized method: {method}")

ValueError: No enabled saver found that supports format='png'

[RobinL]

See the additional requirements here https://github.com/altair-viz/altair_saver/

[NathanHGayle]

@illeamb Thanks for this thread. Update for future readers: Upon opening the saved HTML file there is a PNG download option.

[RobinL]

That's right, thanks. There are also some other options here if you need to automate: #926 (comment)