import matplotlib.pyplot as plt
import matplotlib.widgets as mwidgets
fig, ax = plt.subplots()
ax.plot([1, 2, 3], [10, 50, 100])
def onselect(vmin, vmax):
  print(vmin, vmax)
rectprops = dict(facecolor='blue', alpha=0.5)
span = mwidgets.SpanSelector(ax, onselect, 'horizontal',span_stays=True,
               rectprops=rectprops)
plt.show()

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.widgets import SpanSelector

# Fixing random state for reproducibility
np.random.seed(19680801)

fig, (ax1, ax2) = plt.subplots(2, figsize=(8, 6))
ax1.set(facecolor='#FFFFCC')

x = np.arange(0.0, 5.0, 0.01)
y = np.sin(2*np.pi*x) + 0.5*np.random.randn(len(x))

ax1.plot(x, y, '-')
ax1.set_ylim(-2, 2)
ax1.set_title('Press left mouse button and drag to test')

ax2.set(facecolor='#FFFFCC')
line2, = ax2.plot(x, y, '-')


def onselect(xmin, xmax):
  indmin, indmax = np.searchsorted(x, (xmin, xmax))
  indmax = min(len(x) - 1, indmax)

  thisx = x[indmin:indmax]
  thisy = y[indmin:indmax]
  line2.set_data(thisx, thisy)
  ax2.set_xlim(thisx[0], thisx[-1])
  ax2.set_ylim(thisy.min(), thisy.max())
  fig.canvas.draw()
  
span = SpanSelector(ax1, onselect, 'horizontal', useblit=True, span_stays=True,
          rectprops=dict(alpha=0.5, facecolor='red'))
# Set useblit=True on most backends for enhanced performance.

plt.show()