Adding hover tool tip to bokeh histogram

Question

I have created a histogram in bokeh using the following code:

TOOLS="pan,wheel_zoom,box_zoom,reset,hover"

for column in valid_columns:
    output_file_name = str( file_name + column + ".html" )
    data_values = stats[ column ].tolist()

    output_file( output_file_name )
    histogram, edges = np.histogram( data_values, bins=50 )

    source = ColumnDataSource(
        data = dict( data_value = data_values ) )

    p1 = figure( title = column, background_fill="#E8DDCB", tools=TOOLS )
    p1.quad( top = histogram, bottom = 0, left = edges[ :-1 ], right = edges[ 1: ], 
             fill_color = "#036564", line_color = "#033649" ) 

    hover = p1.select(dict(type=HoverTool))
    hover.tooltips = [ ( "Value", "@data_value" ) ]

    show( p1 )
    print( "Saved Figure to ", output_file_name )   

where valid columns are a list of all columns I want examined within a pandas dataframe. I am trying to add a hover tool tip which will display the number of items stored in each bin but I have not be able to do so. Any help would be appreciated.

Answer 1

If you prefer to not use a ColumnDataSource, you can replace @data_value with @top and it should work with minimal editing:

hover = HoverTool(tooltips = [('Value', '@top')])
p.add_tools(hover)

i.e. editing the example histogram.py in this way also works:

from bokeh.models import HoverTool

def make_plot(title, hist, edges, x, pdf, cdf):
    p = figure(title=title, tools='', background_fill_color="#fafafa")
    p.quad(top=hist, bottom=0, left=edges[:-1], right=edges[1:],
       fill_color="navy", line_color="white", alpha=0.5)
    p.line(x, pdf, line_color="#ff8888", line_width=4, alpha=0.7, legend_label="PDF")
    p.line(x, cdf, line_color="orange", line_width=2, alpha=0.7, legend_label="CDF")

    p.y_range.start = 0
    p.legend.location = "center_right"
    p.legend.background_fill_color = "#fefefe"
    p.xaxis.axis_label = 'x'
    p.yaxis.axis_label = 'Pr(x)'
    p.grid.grid_line_color="white"
    hover = HoverTool(tooltips = [('Density', '@top')])
    p.add_tools(hover)
    return p