Define action on canvas

[cool-RR]

I'm trying to define an action on a canvas:

@Sheet.api
def toggle_plot_asterisk(canvas: Canvas) -> None:
    canvas.options.disp_canvas_charset = '*'

Canvas.addCommand('*', 'toggle-plot-asterisk', 'toggle_plot_asterisk()')

However, when I run it on a plot I get this error: TypeError: toggle_plot_asterisk() missing 1 required positional argument: 'sheet'

Why? A similar pattern works well for BaseSheet.

[saulpw]

Sheet is an alias for TableSheet, which only handles all sheets with rows and columns--a Canvas is actually not a TableSheet. BaseSheet is the ultimate parent sheet class for all "sheets" that get pushed, including Canvases.

If you decorate toggle_plot_asterisk with @Canvas.api instead, it should work. (Note that your first parameter is a Canvas, not a Sheet). The error is confusing, but is because all functions are implicitly globals exposed in .visidatarc, including functions decorated with the monkey-patching .api! The command executor will try the vd and sheet contexts first, but if an identifier isn't on there, it will look in globals; and then fail in this way.

Other ways to get different results (I mention these for completeness but the above fix is the most correct):

• using sheet.toggle_plot_asterisk() in the execstr; this won't fix the problem, but explicitly using sheet will give you the more correct error that the method isn't on the Canvas;
• using @BaseSheet.api; this will work fine and isn't a problem, especially for individual use like in .visidatarc, but is overly broad as it makes the method available on all sheets;
• omitting the @Sheet.api decorator completely and using toggle_plot_asterisk(sheet) (this will work in .visidatarc for the reason mentioned above, but not in a plugin, unless added explicitly with addGlobals()

[cool-RR]

Great, that works, thank you.

Another question: Here's how I wrote the code:

@Canvas.api
def toggle_plot_asterisk(canvas: Canvas) -> None:
    if canvas.options.disp_canvas_charset == '*':
        canvas.options.disp_canvas_charset = DEFAULT_DISP_CANVAS_CHARSET
    else:
        canvas.options.disp_canvas_charset = '*'

I defined DEFAULT_DISP_CANVAS_CHARSET in my code because I couldn't figure out how to get that default value from VisiData. Is that possible?

[saulpw]

That seems fine. You could also do:

DEFAULT_DISP_CANVAS_CHARSET = vd.options.disp_canvas_charset

at the top-level of your code.

[cool-RR]

That's better than my version, thank you. I still think it'll be nice if default values will always be accessible in VisiData code even if they were overridden, but that's not critical.

[cool-RR]

By the way, my stupid hack was to define it this way:

DEFAULT_DISP_CANVAS_CHARSET = lzma.decompress(base64.b64decode('/Td6WFoAAATm1rRGAgAhARYAAAB0L+Wj4AL/APVdAHEoDBAEgdA/tto4kuI0/tYWZYs4kpFqcYNhVWuCYAjoA+51kP/qzYvJ+dlmd2aAk+rB9SBN+ozdt+cviLig0iJrNKjuKVlY2yphXBjNq+09pIXFlJGX+4c+YPaqQchDSHV9MT3qccRZHQZj0KNLafy2c5Of7VNRVe8cx3rtRG9bjKSr8GI20xsQNa4FLs9cbNRFJPaTnhpoH3vDwWQ2mB0KzEAQyz/stMAp/jfosrpfLSXXLsL2bShczRUOX00NqkELz09PltBa93A39jJ4lASWUwrWlTLJ5yGHKtTUCIRFmNg7TPiZs5CYYbj9GEN8qkW1EHR2AAAAALVhmWb/bhXDAAGRAoAGAADSiHuGscRn+wIAAAAABFla')).decode()

Just so the file will be ascii and the line would be as short as possible 😆