How to plot a horizontal line with Matplotlib
• 1 minHorizontal lines are great for showing spots where something happened on the y-axis.
Matplotlib provides the axes.hlines() method to plot horizontal lines.
Here is the example
# For our example dataframe
import pandas as pd
# For our plot
import matplotlib.pyplot as plt
# Generating sample data
df = pd.DataFrame({"col1": range(10)})
# Creating a figure and the axes for our plots
fig, axes = plt.subplots(1,1, figsize=(8,6))
# We plot a hline
axes.hlines(y=2,
xmin=0,
xmax=df["col1"].max())
# We make our canvas tidy and clean
plt.tight_layout()
# We show the graph
plt.show()
And here is the result.

Here you are! You now know how to plot a horizontal line with Matplotlib.
More on plots
If you want to know more about how to add labels, plot different types of plots, etc... check out the other articles I wrote on the topic, just here :
Matplotlib - The Python You Need
We gathered the only Python essentials that you will probably ever need.