Matplotlib 简明教程

Matplotlib - Keypress Event

在计算机编程中，检测和处理 keypress events 是捕捉用户输入和启用应用程序中各种功能的基础。无论是浏览菜单、输入文本、触发动作还是控制交互元素，按键事件在用户交互中起着至关重要的作用。

Matplotlib 提供了处理按键事件的工具，使您能够捕获和响应交互式绘图会话期间的键盘输入。当按下键时，Matplotlib 将触发 key_press_event ，允许用户根据按下的键定义自定义操作。

该库默认附加一些按键回调，以增强交互性。这些默认回调在 Matplotlib 文档的键盘导航快捷方式部分中进行了记录。

Example

让我们看看此基本示例，它演示了 Matplotlib 中的默认按键事件。

import numpy as np
import matplotlib.pyplot as plt

# Define a function to handle keypress events
def press(event):
   print('You pressed:', event.key)

# Create a Matplotlib figure and axis
fig, ax = plt.subplots()

# Connect the keypress event handler to the figure canvas
cid = fig.canvas.mpl_connect('key_press_event', press)

# Plot sin wave
x = np.linspace(0, 10, 100)
ax.plot(x, np.sin(x))

# Display the plot
plt.show()

Output

在执行上述程序时，您将得到以下图像，并且按下任何键以观察此示例的工作 −

keypress event ex1 
You pressed: tab
You pressed: caps_lock
You pressed: shift
You pressed: control
You pressed: alt
You pressed: meta
You pressed: a
You pressed: b
You pressed: c
You pressed: d
You pressed: s
You pressed: g
You pressed: g
You pressed: g
You pressed: g
You pressed: k
You pressed: k
You pressed: k
You pressed: k
You pressed: k
You pressed: k
You pressed: l
You pressed: l
You pressed: p
You pressed: p
You pressed: q

观看下面的视频，了解此按键事件功能在此处的工作方式。

keypress event ex1

从以上输出中，您可以观察到一些默认键，如“g”（切换网格，“s”（保存图像，“q”（关闭图像）等。

Creating a Custom Keypress Event Function

要根据特定需求处理按键事件，您可以创建自定义函数，并使用 mpl_connect 方法将它连接到 key_press_event 。

Example

以下示例演示了一个简单的按键事件函数，当按下“x”键时，该函数切换 x 轴标签的可见性。

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

def 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 points
ax.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()

在执行上述程序时，您将得到以下图像，并且按下任何键以观察此示例的工作 −

keypress event ex2 
Pressed key: x
Pressed key: x
Pressed key: x
Pressed key: x
Pressed key: a
Pressed key: enter

观看下面的视频，了解此按键事件功能在此处的工作方式。

keypress event ex2

Example

这是另一个示例，它演示了如何添加 escape 键来退出图像除了 "q" 键，并且它还会计算 enter 键按下的次数。

import numpy as np
import matplotlib.pyplot as plt

# Define a function to handle keypress events
def 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 canvas
fig.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 counts
result = sum(cnt)
print(result, cnt)

在执行上述程序时，您将得到以下图像，并且按下任何键以观察此示例的工作 −

keypress event ex3 
Pressed key: b
Pressed key: enter
Pressed key: enter
Pressed key: caps_lock
Pressed key: caps_lock
Pressed key: enter
Pressed key: escape
3 [1, 1, 1]
keypress event ex3