showing specific xtick in matplotlib

Question

So I have a graph that runs on an order of magnitude 10000 time steps, and thus I have a lot of data points and the xticks are spaced pretty far apart, which is cool, but I would like to to show on the xaxis the point at which the data is being plotted. In this case the xtick I want to show is 271. So is there a way to just "insert" 271 tick onto the x axis given that I already know what tick I want to display?

Answer 1

If it's not important that the ticks update when panning/zomming (i.e. if the plot is not meant for interactive use), then you can manually set the tick locations with the axes.set_xticks() method. In order to append one location (e.g. 271), you can first get the current tick locations with axes.get_xticks(), and then append 271 to this array.

A short example:

import matplotlib.pyplot as plt
import numpy as np

fig = plt.figure()

ax = fig.add_subplot(111)
ax.plot(np.arange(300))

# Get current tick locations and append 271 to this array
x_ticks = np.append(ax.get_xticks(), 271)

# Set xtick locations to the values of the array `x_ticks`
ax.set_xticks(x_ticks)

plt.show()

This produces

As you can see from the image, a tick has been added for x=271.