Changing r values for cobweb diagrams in Python

Question

Relatively new to Matplotlib. I plotted a cobweb diagram and is now hoping to change the r values via arrow keys as the program is running. Tried to use "import keyboard" along with a "running loop" but it doesn't seem to work. Can someone please explain?

import matplotlib.pyplot as plt
import keyboard
from scipy import linspace

r = 3.35
x0 = 0.3
running = True


def cobweb(f, x0):
    t = linspace(0, 1, 100)
    l = plt.plot(t, f(t))
    plt.plot(t, t)

    x, y = x0, f(x0)
    for _ in range(100):
        fy = f(y)
        plt.plot([x, y], [y, y], 'b', linewidth=1)
        plt.plot([y, y], [y, fy], 'b', linewidth=1)
        x, y = y, fy

    plt.xlabel("X n")
    plt.ylabel("X n+1")
    plt.show()
    plt.close()


while running:
    cobweb(lambda x: r * x * (1 - x), x0)
    if keyboard.is_pressed('up'):
        r += 0.1
    if keyboard.is_pressed('down'):
        r -= 0.1
    cobweb(lambda x: r * x * (1 - x), x0)

Answer 1

You need to turn on the interactive mode with plt.ion() and replace plt.show() with fig.canvas.draw(). Check the following code:

import matplotlib.pyplot as plt
import keyboard
# from scipy import linspace
from numpy import linspace
import time

r = 3.35
x0 = 0.3
running = True


def cobweb(f, x0):
    ax.cla()
    t = linspace(0, 1, 100)
    l = plt.plot(t, f(t))
    plt.plot(t, t)

    x, y = x0, f(x0)
    for _ in range(100):
        fy = f(y)
        plt.plot([x, y], [y, y], 'b', linewidth=1)
        plt.plot([y, y], [y, fy], 'b', linewidth=1)
        x, y = y, fy

    plt.xlabel("X n")
    plt.ylabel("X n+1")
    fig.canvas.draw()
    time.sleep(0.01)

plt.ion()
fig, ax = plt.subplots()

while running:
    if keyboard.is_pressed('up'):
        r += 0.1
    if keyboard.is_pressed('down'):
        r -= 0.1
    cobweb(lambda x: r*x*(1 - x), x0)

By pressing ⇧ or ⇩, you will get plots like these:

Note: if you use linspace by scipy, you get this warning:

DeprecationWarning: scipy.linspace is deprecated and will be removed in SciPy 2.0.0, use numpy.linspace instead

It is wise to replace it with

from numpy import linspace

as I done in the above code. The functionality of your code won't change