Headless mode access to plot by means to save

[sadielbartholomew]

Out plotting functionality creates an illustrative plot for a given configuration, but as an end result it only opens this in a GUI window via (matplotlib's) plt.show() - which doesn't work in a headless context - notably when on remote servers like JASMIN using SSH or in automated scripts. So in these cases, there's no (non-contrived, e.g. without setting up some sort of GUI window support e.g. via X) way to access the plot. Which would become a major deficiency given CATS v2 is targeting HPC/HTC application.

To get around this problem, I suggest we implement the following:

• logic to detect if headless i.e. querying os.environ.get("DISPLAY") or similar, in which case save the plot to the current working directory with a default name;
• an extra config. option --save-plot taking a (path and) filename argument for saving the plot instead of opening it (upon which you do generally get given an option to save from the GUI widgets), as an optional override the user can set.

Happy to take other ideas, though!

[abhidg]

@sadielbartholomew Agreed - we can also support sixel output if the terminal supports it (many modern terminals do), then we can plot directly in the terminal!

[andreww]

Very much like the idea of a save-plot option with or without fancy stuff about detection of the environment.

I imagine this would involve chopping up that plotplan function into something that handles where to do the plotting and something else that gets a matplotlib figure and and axis passed in and actually does the plotting? If so (or even if not) it would be worth adding type annotations to the function arguments.

[sadielbartholomew]

Good point about type annotations, @andreww. Typically in the Python libraries I develop we don't use those (historically we didn't and yet that's one of the few ways we're yet to catch up to modern standards) so I can often forget they exist 😄 But since we use them otherwise consistently here, is particularly good to get them added.

I imagine this would involve chopping up that plotplan function into something that handles where to do the plotting and something else that gets a matplotlib figure and and axis passed in and actually does the plotting?

I would have thought it would be even simpler - no need to touch the plotlplan except to add some logic at the end to either show or save the resulting figure, unless I am missing something?

[sadielbartholomew]

we can also support sixel output if the terminal supports it (many modern terminals do), then we can plot directly in the terminal!

@abhidg ah good thinking! I didn't see your comment until just after I had raised this issue, but yesterday after raising this I put up #173 which I think suggests the same thing (I had to look up what sixel is since I hadn't heard of it before). Now we have the basic plot sorted it would be good to improve our support on remote servers and so on. 🙂

[andreww]

Related note - probably worth doing a function name change as per #171 (comment) as part of this