Segmentation fault when blitting onto closed figure (TkAgg) #16580

Bug report

Bug summary

With the "TkAgg" backend, calling figure.canvas.blit on a closed Figure instance crashes the Python interpreter with "segmentation fault." An easy workaround is to check if the figure is closed using plt.fignum_exists(figure.number) before attempting the blit operation.

I tried a couple other backends and they didn't crash.

Code for reproduction

import numpy as np
import matplotlib.pyplot as plt

fig, axes = plt.subplots()
axes.imshow(np.zeros((1000, 1000, 3), dtype=np.uint8))
fig.canvas.draw()
plt.close(fig.number)
fig.canvas.blit(axes.bbox)

Actual outcome

zsh: segmentation fault (core dumped)  python segfault2.py

Expected outcome

I'm not really sure, but segfaulting the interpreter isn't it. I think an acceptable alternative would be raising a Python exception from within matplotlib.

Matplotlib version

• Operating system: Ubuntu 18.04.4
• Matplotlib version: 3.1.3
• Matplotlib backend: TkAgg
• Python version: 3.6.9

matplotlib was installed from pip in a virtualenv.