python matplotlib: plotting in another process

Question

EDIT: The ultimate requirement for such a Python program is: Receive data from UART from a external circuitry (which probably is equipped with some sensors), the program will process these data, and draw a dynamically updated curve on the computer screen.

So, I want to plot dynamically, the following test script starts a sub-process, and in that process, it accepts data from parent process through a Queue, and plot data accordingly.

But when the script is run, only an empty figure is shown, I can see the console prints "put:" and "got:" messages, meaning both parent and subprocess are running and communicating, but nothing happens in the GUI figure window.

Furthermore, the GUI window is not responsive and if I click on the window, it will crash.

The system is Windows 10, 64 bit. Python version is 2.7 (32bit)

What's the problem here? thank you!

import matplotlib.pyplot as plt
import multiprocessing as mp
import random
import numpy
import time

def worker(q):
    plt.ion()
    ln, = plt.plot([], [])
    plt.show()

    while True:
        obj = q.get()
        n = obj + 0
        print "sub : got:", n

        ln.set_xdata(numpy.append(ln.get_xdata(), n))
        ln.set_ydata(numpy.append(ln.get_ydata(), n))
        plt.draw()

if __name__ == '__main__':
    queue = mp.Queue()
    p = mp.Process(target=worker, args=(queue,))
    p.start()

    while True:
        n = random.random() * 5
        print "main: put:", n
        queue.put(n)
        time.sleep(1.0)

Answer 1

You have to rescale, otherwise nothing will appear:

This works on my computer :

import matplotlib.pyplot as plt
import multiprocessing as mp
import random
import numpy
import time

def worker(q):
    #plt.ion()
    fig=plt.figure()
    ax=fig.add_subplot(111)
    ln, = ax.plot([], [])
    fig.canvas.draw()   # draw and show it
    plt.show(block=False)

    while True:
        obj = q.get()
        n = obj + 0
        print "sub : got:", n

        ln.set_xdata(numpy.append(ln.get_xdata(), n))
        ln.set_ydata(numpy.append(ln.get_ydata(), n))
        ax.relim()

        ax.autoscale_view(True,True,True)
        fig.canvas.draw()

if __name__ == '__main__':
    queue = mp.Queue()
    p = mp.Process(target=worker, args=(queue,))
    p.start()

    while True:
        n = random.random() * 5
        print "main: put:", n
        queue.put(n)
        time.sleep(1.0)