tight_layout throw error: ValueError: max() arg is an empty sequence

Question

I am trying to using plt.ion() in python enable updating the figures:

import numpy as np
import numpy.matlib
import matplotlib.pyplot as plt

plt.ion()

plt.close('all')

tmax =30
W = np.random.rand(6,100)        

fig, ax = plt.subplots(2,3)     
plt.show()

for t in range (1, tmax):
    W = t * W        
    for ii in range(2):
        for jj in range(3):      
            output = W[3*ii+jj,:].reshape((10,10),order = 'F')
            ax[ii,jj].clear()
            ax[ii,jj].imshow(output, interpolation='nearest')                
    plt.tight_layout()
    plt.draw()
    plt.pause(0.1)


plt.waitforbuttonpress()

Running this will show blank figures in console and throw errors:

Traceback (most recent call last):

File "", line 1, in runfile('/Users/Alessi/Documents/Spyder/3240ass/comp.py', wdir='/Users/Alessi/Documents/Spyder/3240ass')

File "/Users/Alessi/anaconda/lib/python3.5/site-packages/spyder/utils/site/sitecustomize.py", line 866, in runfile execfile(filename, namespace)

File "/Users/Alessi/anaconda/lib/python3.5/site-packages/spyder/utils/site/sitecustomize.py", line 102, in execfile exec(compile(f.read(), filename, 'exec'), namespace)

File "/Users/Alessi/Documents/Spyder/3240ass/comp.py", line 27, in plt.tight_layout()

File "/Users/Alessi/anaconda/lib/python3.5/site-packages/matplotlib/pyplot.py", line 1387, in tight_layout fig.tight_layout(pad=pad, h_pad=h_pad, w_pad=w_pad, rect=rect)

File "/Users/Alessi/anaconda/lib/python3.5/site-packages/matplotlib/figure.py", line 1752, in tight_layout rect=rect)

File "/Users/Alessi/anaconda/lib/python3.5/site-packages/matplotlib/tight_layout.py", line 322, in get_tight_layout_figure max_nrows = max(nrows_list)

ValueError: max() arg is an empty sequence

ps.using anaconda spyder

Answer 1

You cannot use interactive more (ion) in a console. Unfortunately the question is not very clear on what you want; but let's suppose you want to show a window with the plot that is animated. An easy way to get that would be to run the script outside an IPython console. In spyder you'd go to Run/Configure (or press F6) and select "Execute in a new dedicated Python console".

Now the problem with the script itself is that you first call plt.show(), which shows empty subplots. This has to be removed.

A version which would show an animation would be

import numpy as np
import matplotlib.pyplot as plt

plt.close('all')
plt.ion()

tmax =30

fig, ax = plt.subplots(2,3)     

for t in range (1, tmax):
    W = np.random.rand(6,100)      
    for ii in range(2):
        for jj in range(3):      
            output = W[3*ii+jj,:].reshape((10,10),order = 'F')
            ax[ii,jj].clear()
            ax[ii,jj].imshow(output, interpolation='nearest')
    if t == 1:                
        plt.tight_layout()
    plt.draw()
    plt.pause(0.1)


plt.waitforbuttonpress()