相对于echarts等基于JavaScript的图表库，matplotlib的交互能力相对较差。
在实际应用中，我们经常想使用十字光标来定位数据坐标，matplotlib内置提供支持。

官方示例

matplotlib提供了官方示例https://matplotlib.org/gallery/widgets/cursor.html

from matplotlib.widgets import Cursorimport numpy as npimport matplotlib.pyplot as plt# Fixing random state for reproducibilitynp.random.seed(19680801)fig = plt.figure(figsize=(8, 6))ax = fig.add_subplot(111, facecolor='#FFFFCC')x, y = 4*(np.random.rand(2, 100) - .5)ax.plot(x, y, 'o')ax.set_xlim(-2, 2)ax.set_ylim(-2, 2)# Set useblit=True on most backends for enhanced performance.cursor = Cursor(ax, useblit=True, color='red', linewidth=2)plt.show()

原理

由源码可知，实现十字光标的关键在于widgets模块中的Cursor类。
class matplotlib.widgets.Cursor(ax, horizOn=True, vertOn=True, useblit=False, **lineprops)

• ax：参数类型matplotlib.axes.Axes，即需要添加十字光标的子图。
• horizOn：布尔值，是否显示十字光标中的横线，默认值为显示。
• vertOn：布尔值，是否显示十字光标中的竖线，默认值为显示。
• useblit：布尔值，是否使用优化模式，默认值为否，优化模式需要后端支持。
• **lineprops：十字光标线形属性， 参见axhline函数支持的属性，https://matplotlib.org/api/_as_gen/matplotlib.axes.Axes.axhline.html#matplotlib.axes.Axes.axhline。

简化案例

光标改为灰色竖虚线，线宽为1。

from matplotlib.widgets import Cursorimport matplotlib.pyplot as pltax = plt.gca()cursor = Cursor(ax, horizOn=False, vertOn= True, useblit=False, color='grey', linewidth=1,linestyle='--')plt.show()

## Cursor类源码

class Cursor(AxesWidget): """ A crosshair cursor that spans the axes and moves with mouse cursor. For the cursor to remain responsive you must keep a reference to it. Parameters ---------- ax : `matplotlib.axes.Axes` The `~.axes.Axes` to attach the cursor to. horizOn : bool, default: True Whether to draw the horizontal line. vertOn : bool, default: True Whether to draw the vertical line. useblit : bool, default: False Use blitting for faster drawing if supported by the backend. Other Parameters ---------------- **lineprops `.Line2D` properties that control the appearance of the lines. See also `~.Axes.axhline`. Examples -------- See :doc:`/gallery/widgets/cursor`. """ def __init__(self, ax, horizOn=True, vertOn=True, useblit=False, **lineprops): AxesWidget.__init__(self, ax) self.connect_event('motion_notify_event', self.onmove) self.connect_event('draw_event', self.clear) self.visible = True self.horizOn = horizOn self.vertOn = vertOn self.useblit = useblit and self.canvas.supports_blit if self.useblit: lineprops['animated'] = True self.lineh = ax.axhline(ax.get_ybound()[0], visible=False, **lineprops) self.linev = ax.axvline(ax.get_xbound()[0], visible=False, **lineprops) self.background = None self.needclear = False def clear(self, event): """Internal event handler to clear the cursor.""" if self.ignore(event): return if self.useblit: self.background = self.canvas.copy_from_bbox(self.ax.bbox) self.linev.set_visible(False) self.lineh.set_visible(False) def onmove(self, event): """Internal event handler to draw the cursor when the mouse moves.""" if self.ignore(event): return if not self.canvas.widgetlock.available(self): return if event.inaxes != self.ax: self.linev.set_visible(False) self.lineh.set_visible(False) if self.needclear: self.canvas.draw() self.needclear = False return self.needclear = True if not self.visible: return self.linev.set_xdata((event.xdata, event.xdata)) self.lineh.set_ydata((event.ydata, event.ydata)) self.linev.set_visible(self.visible and self.vertOn) self.lineh.set_visible(self.visible and self.horizOn) self._update() def _update(self): if self.useblit: if self.background is not None: self.canvas.restore_region(self.background) self.ax.draw_artist(self.linev) self.ax.draw_artist(self.lineh) self.canvas.blit(self.ax.bbox) else: self.canvas.draw_idle() return False

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