No mouseover "x=,y=" for `sns.heatmap` (works only on its colorbar), as if its `ax.format_coords()` was not set

[MestreLion]

This is much better explained in this SO question: Interactive sns.heatmap displays x, y only hovering over the colorbar

The comments suggest this is easy to implement, but I was unable to do so.

It does work fine if you replace the seaborn heatmap() call with direct calls to Matplotlib's pcolormesh() + colorbar(), i.e, instead of:

sns.heatmap(data, ...)

Use this

heat = plt.pcolormesh(data)
plt.colorbar(heat)

So something in Seaborn's usage or customization of Matplotlib's pcolormesh is "unsetting" its default format_coords, which I believe is a bug

[mwaskom]

I don't think this is expected to work, sorry!

[MestreLion]

Preliminary findings:

• This is related to Matplotlib's default behavior when xticklabels/yticklabels are set for pcolormesh: the underlying format_xdata() ends up calling the major tick value formatter, which returns "" for values that are not in the tick labels dictionary.
• Seaborn, by design always populates the tick labels with sensible values, so the mouseover info is always the empty x= y=
• imshow suffers the same problem as pcolormesh, however it sets its artists in a way (mouseover=True perhaps?) that they are queried for additional info, hence the additional [123..] shown on mouseover. But unfortunately Seaborn does not use imshow

Some workarounds that Seaborn could adopt:

• Set ax.fmt_xdata / ax.fmt_ydata, which are None by default, to prevent ax.format_xdata() from falling back to the tick formatter