Add hook for submodules for extensions

[dschwoerer]

Alternative to xHERMES :-)

It allows to use xBOUT for loading any BOUT++ simulation. That way I don't have to think what simulation has generated the data. I just load it, and as long as an appropriate extension is installed, e.g. https://github.com/dschwoerer/xbout.modules.hermes for hermes (as a proof of concept).

After all, I don't want to do something hermes specific. I just want to have decent units ...

If there are some post-processing that would only ever a STORM user do, sure.

But I rather feel the other way round. I would like to have the same interface for my EMC3 simulations and my BOUT++ simulations. But the ones are ds.emc3.* the others ds.bout.* - I want to avoid this to go worse ...

Note that there is a pip bug with submodules and editable installs: pypa/pip#11467

[codecov-commenter]

Codecov Report

Merging #249 (e435cc7) into master (30fa7a7) will decrease coverage by 0.24%.
The diff coverage is 45.45%.

@@            Coverage Diff             @@
##           master     #249      +/-   ##
==========================================
- Coverage   74.11%   73.86%   -0.25%     
==========================================
  Files          13       14       +1     
  Lines        2503     2525      +22     
  Branches      594      609      +15     
==========================================
+ Hits         1855     1865      +10     
- Misses        428      435       +7     
- Partials      220      225       +5     

Impacted Files	Coverage Δ
xbout/load.py	74.00% <27.27%> (-1.31%)	⬇️
xbout/modules/__init__.py	63.63% <63.63%> (ø)
xbout/plotting/animate.py	46.08% <0.00%> (ø)
xbout/plotting/plotfuncs.py	48.27% <0.00%> (ø)

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[bendudson]

Thanks @dschwoerer ! I do agree that a generic solution here would be better, if it can be done.

One thing that can be done is the unit conversion and data labels. xhermes and xstorm use attributes:
units : string containing the SI units e.g. "kg m^2 / s"
conversion : float. Multiply the raw value by this to get SI units
standard_name : A short name like "density", "velocity" that should be standardised
long_name : A longer description suitable for axis labels and legends

e.g.
https://github.com/boutproject/xhermes/blob/main/xhermes/load.py#L67

Those attributes could be in the BOUT.dmp files, enabling automatic conversion

[dschwoerer]

I think that would make most of the pluggins work unnecessary 🎉

Do we want to say "SI" - or are we happy with eV as temperature?

All I would be missing is ds["Te"] = ds.Pe / ds.Ne - not sure this can reasonably be generalised?

The other thing that may be needed is if the log of a quantity is evolved. I think STORM is doing that ...

[ZedThree]

I would say that as long as the units are recognised by UDUNITS or perhaps pint then it should be ok -- eV for temperature should be accepted for instance.

That might also extend to log units too, but I suspect that might be trickier or just not exist in any existing convention -- so you'd either need to just document it somewhere, define new units, or perhaps even just only write out the non-log form?