How to manage text labels in a simple interactive matplotlib plot?

Question

In this code snippet:

import matplotlib.pyplot as plt
import numpy as np

def onclick(event):
  plt.text(event.xdata, event.ydata, f'x', color='black')
  plt.show()

fig, ax = plt.subplots()
fig.canvas.mpl_connect('button_press_event', onclick)
data = np.random.rand(8, 8)
plt.imshow(data, origin='lower', interpolation='None', aspect='equal')
plt.axis('off')
plt.show()

each mouse click leaves an additional letter x on top of the image:

I would like to have only the most recent x shown. How to accomplish it, while keeping it simple?

Paul Jurczak · Accepted Answer · 2022-02-15 22:44:09Z

1

I would recommend you declare a global variable called "txt" or something, and then on click you would first remove the "current" x and add the new one.

txt = None

def onclick(event):
    global txt
    if txt:
        txt.remove()
    txt = plt.text(event.xdata, event.ydata, 'TESTTEST', fontsize=8)
    fig.canvas.draw()

Something like this. It may be messy, But try it.

edited Feb 15, 2022 at 22:44

Paul Jurczak

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answered Feb 15, 2022 at 7:48

Josip Juros

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4 Comments

Paul Jurczak Over a year ago

Thanks. It works after a correction: if txt: txt.remove(). The first fig.canvas.draw() is not necessary.

Josip Juros Over a year ago

@PaulJurczak Nice, Glad to be of help :)

Paul Jurczak Over a year ago

Do you know, by the chance, how to remove all text added to the plot with one matplotlib function call? What is the data structure holding references to the text?

Josip Juros Over a year ago

@PaulJurczak If I remember correctly doing plot.texts should return a List or Tuple of all texts on the plot.

Paul Jurczak · Accepted Answer · 2022-05-27 00:14:39Z

0

The text objects are stored internally by matplotlib. The ones created by plt.text() can be removed. Here is the original code snippet, modified to accomplish this:

import matplotlib.pyplot as plt
import matplotlib.text as text
import numpy as np

def onclick(event):
  for x in plt.findobj(match=text.Text):
    try:
      x.remove()
    except NotImplementedError:
      pass

  plt.text(event.xdata, event.ydata, f'x', color='black')
  plt.show()

fig, ax = plt.subplots()
fig.canvas.mpl_connect('button_press_event', onclick)
data = np.random.rand(8, 8)
plt.imshow(data, origin='lower', interpolation='None', aspect='equal')
plt.axis('off')
plt.show()

edited May 27, 2022 at 0:14

answered May 26, 2022 at 17:51

Paul Jurczak

8,6284 gold badges52 silver badges98 bronze badges

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