RuntimeError: Cannot open figure

RuntimeError: Cannot open figure

$ python -c "import matplotlib.pyplot as plt; plt.figure(); plt.show()"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
RuntimeError: Cannot open figure

Why this happens

A GUI backend isn’t available in the current environment.

Fix

Switch to a compatible backend or save figures to files.

Wrong code

import matplotlib.pyplot as plt
plt.figure()
plt.show()

Fixed code

import matplotlib
matplotlib.use('Agg')
import matplotlib.pyplot as plt
plt.figure()
plt.savefig('figure.png')