Real time matplotlib plot is not working while still in a loop

Question

I want to create a real time graph plotting program which takes input from serial port. Initially, I had tried a lot of code that posted on websites, but none of them worked. So, I decided to write code on my own by integrating pieces of code I've seen on the websites. But the problem is the graph will pop out only when the program ends,in other words, out of the loop. While in the loop, it shows nothing, just a blank canvas. I'm still pretty new to python. Here is my code.

import matplotlib.pyplot as plt
import time
import random
from collections import deque
import numpy as np

# simulates input from serial port
def random_gen():
    while True:
        val = random.randint(1,10)
        yield val
        time.sleep(0.1)


a1 = deque([0]*100)
ax = plt.axes(xlim=(0, 20), ylim=(0, 10))
d = random_gen()

line, = plt.plot(a1)
plt.ion()
plt.ylim([0,10])
plt.show()

for i in range(0,20):
    a1.appendleft(next(d))
    datatoplot = a1.pop()
    line.set_ydata(a1) 
    plt.draw()
    print a1[0]
    i += 1
    time.sleep(0.1)

Also, I use Enthought Canopy academic license ver 1.1.0.

Answer 1

Here is the solution add this plt.pause(0.0001) in your loop as below:

import matplotlib.pyplot as plt
import time
import random
from collections import deque
import numpy as np

# simulates input from serial port
def random_gen():
    while True:
        val = random.randint(1,10)
        yield val
        time.sleep(0.1)


a1 = deque([0]*100)
ax = plt.axes(xlim=(0, 20), ylim=(0, 10))
d = random_gen()

line, = plt.plot(a1)
plt.ion()
plt.ylim([0,10])
plt.show()

for i in range(0,20):
    a1.appendleft(next(d))
    datatoplot = a1.pop()
    line.set_ydata(a1)
    plt.draw()
    print a1[0]
    i += 1
    time.sleep(0.1)
    plt.pause(0.0001)                       #add this it will be OK.