There are many visualisation libraries in python out there and altair offers some original features. It offers a wide variety of charts, a grammar-like api, loads of interactivity features and the option of exporting directly to the browser.
Here's how you can add the tooltip.
(alt.Chart(plot_df) .mark_point(color='black') .encode(x='yday', y='births', tooltip=['date', 'births', 'wday']) .properties(width=600, height=300) .interactive())
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