Fading updating 3D plot

cont_depth_plot.py

import numpy as np
import matplotlib.pyplot as plt
from mpl_toolkits.mplot3d import proj3d

def main():
    fig = plt.figure()
    ax = fig.add_subplot(111, projection='3d')

    ax.set_ylim(-100, 100)
    ax.set_xlim(-10, 10)
    ax.set_zlim(-100, 100)

    plt.ion()
    plt.show()

    x = np.arange(-50, 51)
    lines = []
    num_l = 4
    plot_cols = ["r", "g", "y", "b"]

    for l_i in range(num_l):
        lines.append(
            ax.plot([], [], [], c=plot_cols[l_i])[0])

    for y in np.arange(1, 30, 3):
        z = x**2 + y

        for l_i, line in enumerate(lines):
            line.set_data(x, 0)
            line.set_3d_properties(z+l_i*10)
            line.set_alpha((num_l-l_i)/num_l)

        plt.draw()
        plt.pause(0.001)
        input("Press [enter] to continue.")

if __name__ == '__main__':
    main()