Add calculated Bands or Spans corresponding x-axis categories

Hi, I believe I have encountered this issue, but want to check. Cross-posted on SO here.

Let’s say I want to add horizontal lines on my chart which correspond to the median value of some group, or a standard deviation band. For example, the median number of apples sold. (Thanks to previous posters who helped with this; you’ll recognize this toy problem.) Is this possible in Bokeh? Is it possible in any Python plotting library?

import pandas as pd
from bokeh.io import output_notebook, show, reset_output
from bokeh.palettes import Spectral5, Turbo256
from bokeh.plotting import figure
from bokeh.transform import factor_cmap
from bokeh.models import Band, Span, FactorRange, ColumnDataSource

fruits = ['Apples', 'Pears']
years = ['2015', '2016']

data = {'fruits' : fruits,
        '2015'   : [2, 1],
        '2016'   : [5, 3]}

fruit_df = pd.DataFrame(data).set_index("fruits")
tidy_df = (pd.DataFrame(data)
           .melt(id_vars=["fruit"], var_name="year")
           .assign(fruit_year=lambda df: list(zip(df['fruit'], df['year'])))
           .set_index('fruit_year'))

Now on to making the figure…

p = figure(x_range=FactorRange(factors=tidy_df.index.unique()),
           plot_height=400,
           plot_width=400,
           tooltips=[('Fruit', '@fruit'), # first string is user-defined; second string must refer to a column
                     ('Year', '@year'),
                     ('Value', '@value')])

cds = ColumnDataSource(tidy_df)

index_cmap = factor_cmap("fruit", 
                         Spectral5[:2], 
                         factors=sorted(tidy_df["fruit"].unique())) # this is a reference back to the dataframe

p.circle(x='fruit_year', 
         y='value', 
         size=20,
         source=cds,
         fill_color=index_cmap,
         line_color=None,
        )
# how do I add a median just to one categorical section?
median = Span(location=tidy_df.loc[tidy_df["fruit"] == "Apples", "value"].median(), # median value for Apples
              #dimension='height', 
              line_color='red',
              line_dash='dashed', 
              line_width=1.0
             )

p.add_layout(median)

# how do I add this standard deviation(ish) band to just the Apples or Pears section?
band = Band(
    base='fruit_year',
    lower=2,
    upper=4,
    source=cds,
)

p.add_layout(band)

show(p)

Output:

Here’s what I want, done quickly in Tableau:

Is there a way to make this happen? Thank you!

Thank you for linking this post from the SO post. However, in the future it would be helpful to link the SO post from a Discourse post as well.
With that being said, I have answered the question on SO: https://stackoverflow.com/a/61929693/564509