python matplotlib

Matplotlib Cursor — How to Add a Cursor and Annotate Your Plot

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

#x and y arrays for defining an initial function
x = np.linspace(0, 10, 100)
y = np.exp(x**0.5) * np.sin(5*x)

# Plotting
fig = plt.figure()
ax = fig.subplots()
ax.plot(x,y, color = 'b')
ax.grid()

# Defining the cursor
cursor = Cursor(ax, horizOn=True, vertOn=True, useblit=True,
                color = 'r', linewidth = 1)

# Creating an annotating box
annot = ax.annotate("", xy=(0,0), xytext=(-40,40),textcoords="offset points",
                    bbox=dict(boxstyle='round4', fc='linen',ec='k',lw=1),
                    arrowprops=dict(arrowstyle='-|>'))
annot.set_visible(False)

# Function for storing and showing the clicked values
coord = []
def onclick(event):
    global coord
    coord.append((event.xdata, event.ydata))
    x = event.xdata
    y = event.ydata

    # printing the values of the selected point
    print([x,y])
    annot.xy = (x,y)
    text = "({:.2g}, {:.2g})".format(x,y)
    annot.set_text(text)
    annot.set_visible(True)
    fig.canvas.draw() #redraw the figure


fig.canvas.mpl_connect('button_press_event', onclick)
plt.show()

# Unzipping the coord list in two different arrays
x1, y1 = zip(*coord)
print(x1, y1)