Add interactive cursors

[folkien]

Example code

import matplotlib.pyplot as plt
import numpy as np

class Cursor(object):
def init(self, ax):
self.ax = ax
self.lx = ax.axhline(color='k') # the horiz line
self.ly = ax.axvline(color='k') # the vert line

    # text location in axes coords
    self.txt = ax.text(0.7, 0.9, '', transform=ax.transAxes)

def mouse_move(self, event):
    if not event.inaxes:
        return

    x, y = event.xdata, event.ydata
    # update the line positions
    self.lx.set_ydata(y)
    self.ly.set_xdata(x)

    self.txt.set_text('x=%1.2f, y=%1.2f' % (x, y))
    self.ax.figure.canvas.draw()

class SnaptoCursor(object):
"""
Like Cursor but the crosshair snaps to the nearest x, y point.
For simplicity, this assumes that x is sorted.
"""

def __init__(self, ax, x, y):
    self.ax = ax
    self.lx = ax.axhline(color='k')  # the horiz line
    self.ly = ax.axvline(color='k')  # the vert line
    self.x = x
    self.y = y
    # text location in axes coords
    self.txt = ax.text(0.7, 0.9, '', transform=ax.transAxes)

def mouse_move(self, event):
    if not event.inaxes:
        return

    x, y = event.xdata, event.ydata
    indx = min(np.searchsorted(self.x, x), len(self.x) - 1)
    x = self.x[indx]
    y = self.y[indx]
    # update the line positions
    self.lx.set_ydata(y)
    self.ly.set_xdata(x)

    self.txt.set_text('x=%1.2f, y=%1.2f' % (x, y))
    print('x=%1.2f, y=%1.2f' % (x, y))
    self.ax.figure.canvas.draw()

t = np.arange(0.0, 1.0, 0.01)
s = np.sin(2 * 2 * np.pi * t)

fig, ax = plt.subplots()
ax.plot(t, s, 'o')
cursor = Cursor(ax)
fig.canvas.mpl_connect('motion_notify_event', cursor.mouse_move)

fig, ax = plt.subplots()
ax.plot(t, s, 'o')
snap_cursor = SnaptoCursor(ax, t, s)
fig.canvas.mpl_connect('motion_notify_event', snap_cursor.mouse_move)

plt.show()