Bokeh HoverTool datetime formatter not working

Question

My code for the bokeh HoverTool is the following:

p = figure(
        plot_height=250,
        x_axis_type='datetime',
    )
p.vbar(x=data_df['date'].dt.to_pydatetime(), top=data_df['data'].values, width=datetime.timedelta(1))
hover_tool = HoverTool(
        tooltips=[('Count', '@top'), ('Date', '@x')], mode='vline', formatters={'$x': 'datetime'}
    )
p.add_tools(hover_tool)

I still get the numeric format of the date as can be seen on the image. I tried formatters={'@x': 'datetime'} with no luck.

Answer 1

Your solution works, if you use $x instead of @x and add one of the listed formats supported by the DatetimeTickFormatter to ('Date', '$x') like ('Date', '$x{%F}'). There are plenty of options and you can select the one you prefere the most.

Minimal Example

import pandas as pd
from bokeh.plotting import show, figure, output_notebook
from bokeh.models import HoverTool, ColumnDataSource
output_notebook()

data_df = pd.DataFrame({'date':pd.date_range('2022-05-13', freq='D', periods=10), 'top':list(range(10))})

p = figure(
        plot_height=250,
        x_axis_type='datetime',
    )
p.vbar(x=data_df['date'], top=data_df['top'], width=pd.Timedelta('12H'))
hover_tool = HoverTool(
        tooltips=[('Count', '@top'), ('Date', '$x{%F}')], mode='vline', formatters={"$x": "datetime"}
    )
p.add_tools(hover_tool)
show(p)

Comment:

I don't know why there is no working default, but maybe because there are so many options, that any default would be somehow wrong.