There’s a decent chance there was an exception or error — in the browser’s JavaScript console. The fact of the matter is that the vast majority of actual work in Bokeh is not done in Python, it is done by the BokehJS JavaScript library.
We can’t issue an error for simply creating a LinearColorMapper with initial empty palette, because it’s not actually an error until it hits BokehJS, and a user could update the value between creating and calling “show”. There is a validation mechanism that can catch things at serialization (“show”) time, but it’s clunky and adds expense, so we try to avoid it except for very common problems (and this is the first time this has been raised on a help forum in ~10 years).
It’d probably be more fruitful to find a way to surface BokehJS errors more visibly than just the browser console, which not all users know to check. Please feel free to open a GitHub development discussion about this topic.
Good point, thanks Bryan. What’s this JavaScript thing I keep hearing about?
But yes, for folks like me who are blissfully ignorant of what’s happening under bokeh’s magic hood - and forget that browsers have consoles! - having some way to make errors on the JS side more visible sounds like it would be helpful. Realize this is probably rare, though.
I will attempt to open a GitHub request and probably garble it. Will edit this post with link.
