[FIXED] How to update a shape on Matplotlib?

Issue

I have a rectangular shape which is drawn on an image. I would like to move that shape around, ie change its coordinates, plot the new shape and remove the old one (the background image stays the same)

Something similar to this code. It shows a rectangle three times but I want when the green shape is drawn, the red one to be deleted and similarly for the blue. When the blue appears to remove the green.

import matplotlib.pyplot as plt
import numpy as np

# Get an example image
image_file = r"image_splash.jpg"
img = plt.imread(image_file)

# Make some example data
x = np.array([475, 475, 675, 675, 475])
y = np.array([100, 200, 200, 100, 100])

# Create a figure
_dpi = 72
fig = plt.figure(1, figsize=(1000/_dpi, 1000/_dpi), dpi=_dpi)
ax = fig.add_subplot(1, 1, 1)
ax.set_aspect('equal')

# Show the image
ax.imshow(img)

# Now, loop through the offset array and update the shape 
# (This obviously doesnt work, it plots all three shapes)
rgb = ['r', 'g', 'b']
offset = [0, 150, 300]
plt.plot(x, y + offset[0], c=rgb[0]) # draw the red rect
plt.plot(x, y + offset[1], c=rgb[1]) # should remove the red and draw the green
plt.plot(x, y + offset[2], c=rgb[2]) # should remove the green and draw the blue

Solution

You can try the animation api of matplotlib like shown below

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.animation import FuncAnimation

fig, ax = plt.subplots()
xdata, ydata = [], []
(ln,) = plt.plot([], [], "r")

x = np.array([475, 475, 675, 675, 475])
y = np.array([100, 200, 200, 100, 100])
offset = [0, 150, 300]
colors = {
    0: "red",
    150: "green",
    300: "blue",
}


def init():
    ax.set_xlim(0, 1000)
    ax.set_ylim(0, 1000)
    return (ln,)


def update(_offset):
    ln.set_data(x, y + _offset)
    ln.set_color(colors[_offset])
    return (ln,)


def gety():
    for i in range(1000):
        yield offset[i % 3]


ani = FuncAnimation(fig, update, frames=gety(), init_func=init, blit=True)
plt.show()

Answered By - abhilb