Realtime Subplots Updating - matplotlib

Question

The following code works well for me to display and update in real time on one chart data coming from 2 sources:
import matplotlib.pyplot as plt
import random
import time
fig = plt.gcf()
fig.set_size_inches(12, 6) # width and height in inches
fig.show()
i=1
x, y1, y2 = [], [],[]
x_scale = 30
plt.ylabel('random')
plt.xlabel('Sample')
plt.ylim(top = 100, bottom = 0)
while True:
if len(x) > x_scale:
x.pop(0)
y1.pop(0)
y2.pop(0)
x.append(i)
y1.append(round(100*random.random()))
y2.append(round(10*random.random()))
plt.plot(x,y1, color = 'b')
plt.plot(x,y2, color = 'r')
plt.xlim(left=i-x_scale, right=i)
fig.canvas.draw()
if plt.waitforbuttonpress(0.1): break # this will wait 0.1 seconds for your keypress
i += 1
I need to do something similar, this time plotting separate data on separate charts. The following code based on the above is not working:
import matplotlib.pyplot as plt
import random
x, y1, y2 =[],[],[]
x_scale=30
i=0
fig, (ax1, ax2) = plt.subplots(2,sharex=True)
ax1.set_title("top chart")
ax2.set_title("bottom chart")
plt.show()
while i<40:
if len(x) > x_scale:
x.pop(0)
y1.pop(0)
y2.pop(0)
x.append(i)
plt.xlim(left=i-x_scale, right=i)
y1.append(round(100*random.random()))
y2.append(round(10*random.random()))
ax1.plot(x,y1)
ax2.plot(x,y2)
plt.draw()
i+=2
Any suggestions please.

Answer 1

Following DavidG's suggestion and some further experimentation here follows the code which in the end worked for me:
import matplotlib.pyplot as plt
import random
x, y1, y2 =[],[],[]
x_scale=30
i=0
fig, (ax1, ax2) = plt.subplots(2,sharex=True)
fig.set_size_inches(15, 8) # width and height in inches
ax1.set_title("top chart")
ax2.set_title("bottom chart")
ax2.set_xlabel("TIME")
ax1.set_ylabel("RND_1")
ax2.set_ylabel("RND_2")
while True:
if len(x) > x_scale:
x.pop(0)
y1.pop(0)
y2.pop(0)
x.append(i)
ax1.set_xlim(i-x_scale, i)
ax2.set_xlim(i-x_scale, i)
ax1.set_ylim(0, 150)
ax2.set_ylim(0, 20)
y1.append(round(100*random.random()))
y2.append(round(10*random.random()))
ax1.plot(x,y1, color = 'b')
ax2.plot(x,y2, color = 'r')
plt.draw()
# plt.pause(0.01)
if plt.waitforbuttonpress(0.01): break # this will wait 0.1 seconds for your keypress
i+=1
Instead of the plt.pause() I used the plt.waitforbuttonpress() which accomplished the same job but also enabled me to use an infinite loop for continuous plotting yet allows me to exit neatly by pressing esc when I want to. The anomalous issue with the x axis I reported was resolved by removing a command which I had inserted earlier whilst searching for a solution.
I hope someone may find this useful.
cheers