Matplotlib - Keypress Event (2024)

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In computer programming, the detection and handling of keypress events are fundamental for capturing user input and enabling various functionalities within applications. Whether it's navigating through menus, entering text, triggering actions, or controlling interactive elements, keypress events play a crucial role in user interaction.

Matplotlib provides the tools for handling the keypress events, allowing you to capture and respond to keyboard inputs during interactive plotting sessions. When a key is pressed, Matplotlib triggers the key_press_event, allowing users to define custom actions based on the pressed keys.

The library attaches some keypress callbacks by default for enhanced interactivity. These default callbacks are documented in the Navigation keyboard shortcuts section of the Matplotlib documentation.

Example

Let's see this basic example, which demonstrates the default keypress events in Matplotlib.

import numpy as npimport matplotlib.pyplot as plt# Define a function to handle keypress eventsdef press(event): print('You pressed:', event.key)# Create a Matplotlib figure and axisfig, ax = plt.subplots()# Connect the keypress event handler to the figure canvascid = fig.canvas.mpl_connect('key_press_event', press)# Plot sin wavex = np.linspace(0, 10, 100)ax.plot(x, np.sin(x))# Display the plotplt.show()

Output

On executing the above program you will get the following figure, and press any key to observe the working of this example −

You pressed: tabYou pressed: caps_lockYou pressed: shiftYou pressed: controlYou pressed: altYou pressed: metaYou pressed: aYou pressed: bYou pressed: cYou pressed: dYou pressed: sYou pressed: gYou pressed: gYou pressed: gYou pressed: gYou pressed: kYou pressed: kYou pressed: kYou pressed: kYou pressed: kYou pressed: kYou pressed: lYou pressed: lYou pressed: pYou pressed: pYou pressed: q

Watch the video below to observe how this keypress event feature works here.

From the above output, you can observe the working of some of the default keys like 'g' (toggling the grid), 's' (saving the figure), 'q' (closing the figure), and more.

Creating a Custom Keypress Event Function

To handle keypress events to specific needs, you can create a custom function and connect it to the key_press_event using the mpl_connect method.

Example

The following example demonstrates a simple keypress event function that toggles the visibility of an xlabel when the 'x' key is pressed.

import sysimport matplotlib.pyplot as pltimport numpy as npdef on_press(event): print('Pressed key:', event.key) sys.stdout.flush() # Toggle visibility of xlabel when 'x' key is pressed if event.key == 'x': visible = xl.get_visible() xl.set_visible(not visible) fig.canvas.draw()fig, ax = plt.subplots()fig.canvas.mpl_connect('key_press_event', on_press)# Plot random data pointsax.plot(np.random.rand(12), np.random.rand(12), 'go')xl = ax.set_xlabel('Toggle this label when the "x" key is pressed', fontsize=16, color='red')ax.set_title('Press x key')plt.show()

Output

On executing the above program you will get the following figure, and press any key to observe the working of this example −

Pressed key: xPressed key: xPressed key: xPressed key: xPressed key: aPressed key: enter

Watch the video below to observe how this keypress event feature works here.

Example

Here is another example that demonstrates how to add the escape key to exit the figure in addition to the "q" key and also it calculates the how many number of times the enter key is pressed.

import numpy as npimport matplotlib.pyplot as plt# Define a function to handle keypress eventsdef press(event): print('Pressed key:', event.key) # If the 'enter' key is pressed, append 1 to the count list if event.key == 'enter': cnt.append(1) # If the 'escape' key is pressed, close the plot if event.key == "escape": plt.close()cnt = []# Create a figure fig, ax = plt.subplots()# Connect the keypress event handler to the figure canvasfig.canvas.mpl_connect('key_press_event', press)ax.plot(np.random.rand(12), np.random.rand(12), 'go')plt.show()# Calculate and print the sum of countsresult = sum(cnt)print(result, cnt)

Output

On executing the above program you will get the following figure, and press any key to observe the working of this example −

Pressed key: bPressed key: enterPressed key: enterPressed key: caps_lockPressed key: caps_lockPressed key: enterPressed key: escape3 [1, 1, 1]