I like Altair, and have built a couple analyses and products with it. In general, it's a convenient way to do exploratory data analysis. But I have found it to be sort of inflexible for simple variations on common chart types -- especially if you want to augment a chart with information that is not in the dataframe instance used to instantiate the altair.Chart object. For instance, if you want to draw a line overlay on a chart, the best way to do it (to my knowledge) is append the start and end coordinates to your dataframe before calling mark_line().

I'm curious whether anyone else has had similar frustrations? I wonder what enhancements might make practical use of Altair for those use cases easier.