Matplotlib - Close Event

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In the context of programming and software design, an event refers to an action or incident that is identified by the software. These events can be initiated by the system, user inputs, or other sources and are subject to handling by the software.

Specifically, a close event is an occurrence triggered when a figure is closed within the software interface. This event means the termination or closure of the graphical representation or window associated with the figure and reminds the software to respond accordingly.

Close Events in Matplotlib

Matplotlib provides a set of tools to handle events, among them is the ability to handle close events. A close event in Matplotlib occurs when a figure window is closed, triggering specific actions within your Python script. By connecting to the close_event you can execute custom code in response to a figure being closed.

In this tutorial, we will explore how to use close events in Matplotlib to enhance interactive plots.

Example

Here is a simple example that displays a message when the user closes the figure.

import matplotlib.pyplot as plt

def on_close(event):
   print('The Figure is Closed!')

fig, ax = plt.subplots(figsize=(7, 4))
ax.annotate('X', xy=(1, 1), xytext=(0.9, 0.65), fontsize=20,
   arrowprops=dict(facecolor='red'),
   horizontalalignment='left',
   verticalalignment='bottom')

fig.canvas.mpl_connect('close_event', on_close)

ax.text(0.15, 0.5, 'Close This Figure!', dict(size=30))
plt.show()

Output

On executing the above code we will get the following output −

After closing the above output figure, the following message is displayed in the console −

The Figure is Closed!

Detecting Closed Axes

When dealing with multiple axes in a figure, you need to determine if a specific axis has been closed you can use the close event action in Matlotlib.

Example

Here is an example that demonstrates how to determine if a specific axis has been closed or not, using the close event in Matplotlib.

import matplotlib.pyplot as plt

# Function to handle the event 
def on_close(event):
   event.canvas.figure.axes[0].has_been_closed = True
   print('The Figure is Closed!')

# Create the figure 
fig, ax = plt.subplots(figsize=(7, 4))
ax.set_title('Detecting Closed Axes')
ax.has_been_closed = False
ax.plot(range(10))

# connect the event with the callable function
fig.canvas.mpl_connect('close_event', on_close)

plt.show()
print('Check the attribute has_been_closed:', ax.has_been_closed)

Output

On executing the above program you will get the following output −

After closing the above output figure, the following message is displayed in the console −

The Figure is Closed!
Check the attribute has_been_closed: True

Continuing Code After Closing

In some cases, it may be necessary for your code to continue running even after the figure is closed (close event triggered). This is particularly useful for background processes or animations.

Example

The following example demonstrates how to continue code execution after the figure is closed.

import matplotlib.pyplot as plt
import matplotlib.animation as animation
import numpy as np
import time

close_flag = 0

def handle_close(evt):
   global close_flag
   close_flag = 1
   print('The Figure is Closed!')

# Activate interactive mode
plt.ion()  
fig, ax = plt.subplots()

# listen to close event
fig.canvas.mpl_connect('close_event', handle_close)

# Generating x values 
x = np.arange(0, 2*np.pi, 0.01)
y = np.sin(x)

# Plotting the initial sine curve
line, = ax.plot(x, y)
ax.legend([r'$\sin(x)$'])

# Function to update the plot for each frame of the animation
def update(frame):
   line.set_ydata(np.sin(x + frame / 50))
   return line

t = 0
delta_t = 0.1
while close_flag == 0:
   if abs(t - round(t)) < 1e-5:
      print(round(t))
    
   x = x + delta_t
   y = y - delta_t

   # Creating a FuncAnimation object
   ani = animation.FuncAnimation(fig=fig, func=update, frames=40, interval=30)

   # draw the figure
   fig.canvas.draw() 
   fig.canvas.flush_events() 

   # wait a little bit of time
   time.sleep(delta_t) 

   t += delta_t

   if close_flag == 1:
      break

print('ok')

Output

On executing the above program you will get the following output −

After closing the above output figure, the following message is displayed in the console −

0
1
2
3
4
5
The Figure is Closed!
ok

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