Plot a vertical line using matplotlib

Question

I would like to draw a vertical line with Matpotlib and I\'m using axvline, but it doesn\'t work.

import sys
import matplotlib
matplotlib.use(\         


        

Answer 1

matplotlib.pyplot.vlines

• The difference is that you can pass multiple locations for x as a list, while matplotlib.pyplot.axvline only permits one location.
  • Single location: x=37
  • Multiple locations: x=[37, 38, 39]
• If you're plotting a figure with something like fig, ax = plt.subplots(), then replace plt.vlines or plt.axvline with ax.vlines or ax.axvline, respectively.

import numpy as np
import matplotlib.pyplot as plt

xs = np.linspace(1, 21, 200)
plt.vlines(x=[37, 38, 39], ymin=0, ymax=len(xs), colors='purple', ls='--', lw=2, label='vline_multiple')
plt.vlines(x=40, ymin=0, ymax=len(xs), colors='green', ls=':', lw=2, label='vline_single')
plt.axvline(x=36, color='b', label='avline')
plt.legend()
plt.show()

Answer 2

Your example is not self contained, but I think you need to replace:

plt.axvline(x=4)

with:

ax.axvline(x=4)

You are adding the line to an axis that you are not displaying. Using plt. is the pyplot interface which you probably want to avoid for a GUI. So all your plotting has to go on an axis like ax.