import numpy as np
import holoviews as hv
from holoviews import opts
hv.extension('bokeh')
The HLine element is a type of annotation that marks a position along the y-axis. Here is an HLine element that marks the mean of a points distributions:
xs = np.random.normal(size=100)
ys = np.random.normal(size=100) * xs
overlay = hv.Points((xs,ys)) * hv.HLine(ys.mean())
overlay.opts(
opts.HLine(color='blue', line_width=6),
opts.Points(color='#D3D3D3'))
For full documentation and the available style and plot options, use hv.help(hv.HLine).