Any way to create a legend title in Bokeh?

Question

Is there any way to add a title to legends, e.g. current legend on the left, legend with title on the right. This particular legend is placed outside the plot are so I don't know if I can fake it with a text glyph.

Answer 1

As of the latest version of Bokeh (1.2) you can add a title to your legend as follows:

import numpy as np

from bokeh.layouts import gridplot
from bokeh.plotting import figure, show, output_file

x = np.linspace(0, 4*np.pi, 100)
y = np.sin(x)

TOOLS = "pan,wheel_zoom,box_zoom,reset,save,box_select"

p1 = figure(title="Legend Example", tools=TOOLS)

p1.circle(x,   y, legend="sin(x)")
p1.circle(x, 2*y, legend="2*sin(x)", color="orange")
p1.circle(x, 3*y, legend="3*sin(x)", color="green")

p1.legend.title = 'Example Title'

p2 = figure(title="Another Legend Example", tools=TOOLS)

p2.circle(x, y, legend="sin(x)")
p2.line(x, y, legend="sin(x)")

p2.line(x, 2*y, legend="2*sin(x)", line_dash=(4, 4), line_color="orange", line_width=2)

p2.square(x, 3*y, legend="3*sin(x)", fill_color=None, line_color="green")
p2.line(x, 3*y, legend="3*sin(x)", line_color="green")

output_file("legend.html", title="legend.py example")

show(gridplot([p1, p2], ncols=2, plot_width=400, plot_height=400)) 

This code was taken from the official docs

Answer 2

I found that still in the Bokeh library they do not implement a way to add a title to the legend but a solution that I implement is the following: Add a very small white dot before adding any other chart.

Example_Code:

import numpy as np
from bokeh.plotting import output_file, figure, show

x = np.linspace(0, 4*np.pi, 100)
y = np.sin(x)
legend_title = "Math Functions" #Legend Title 

output_file("legend_labels.html")

p = figure()

p.circle(0, 0, size=0.00000001, color= "#ffffff", legend=legend_title)

p.circle(x, y, legend="sin(x)")
p.line(x, y, legend="sin(x)")

p.line(x, 2*y, legend="2*sin(x)",
   line_dash=[4, 4], line_color="orange", line_width=2)

p.square(x, 3*y, legend="3*sin(x)", fill_color=None, line_color="green")
p.line(x, 3*y, legend="3*sin(x)", line_color="green")

p.legend.label_text_font = "times"
p.legend.label_text_font_style = "italic"
p.legend.label_text_color = "navy"

show(p)