Matplotlib ion() function fails to be interactive

Question

I have problem with interactive feature of Matplotlib. I ran the following program and received a freezing empty graph window.

import matplotlib.pyplot as pl         


        

Answer 1

I bumped into this link found here, which answers my problem.

It seems that after turning on interactive mode through plt.ion(), pyplot needs to be paused temporarily for it to update/redraw itself through plt.pause(0.0001). Here is what I did and it works!

>>> import matplotlib.pyplot as plt
>>> import numpy as np
>>> plt.ion()
>>> x = np.arange(0, 4*np.pi, 0.1)
>>> y = [np.sin(i) for i in x]
>>> plt.plot(x, y, 'g-', linewidth=1.5, markersize=4)
>>> plt.pause(0.0001)         
>>> plt.plot(x, [i**2 for i in y], 'g-', linewidth=1.5, markersize=4)
>>> plt.pause(0.0001)
>>> plt.plot(x, [i**2*i+0.25 for i in y], 'r-', linewidth=1.5, markersize=4) 
>>> plt.pause(0.0001)

If you tried that in your IDLE console, notice that up to this point everything got displayed except that the graph window freezes and cannot exit. To unfreeze it type the following last statement

>>> plt.show(block=True)

Now the window can be closed.