Documentation Link

https://matplotlib.org/devdocs/api/figure_api.html?highlight=figure%20show#matplotlib.figure.Figure.show

Problem

From the linked documentation

Proper use cases for Figure.show include running this from a GUI application or an IPython shell.

If you're running a pure python shell or executing a non-GUI python script, you should use matplotlib.pyplot.show instead, which takes care of managing the event loop for you.

I have just checked, and figure.show() works ALSO in a pure python shell (here it's 3.9, in Suse Tumbleweed).

Suggested improvement

Specify that after version 3.x (??) of the interpreter the event loop is managed also by a vanilla Python REPL.

Matplotlib Version

3.5.1