Problems when switching matplotlib backends

[YuccaTang]

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I was switching backends when using Jupyter notebook to save or display figures.

I first used matplotlib.use('inline') to display the figures, then I used matplotlib.use('agg') to save figures. It was ok even when I returned to recall matplotlib.use('inline') to show figures.

The problem is that when I first called matplotlib.use('agg') to save figures and then used matplotlib.use('inline'), the figures didn't show up. What I got was only something like <Figure size 640x480 with 1 Axes>.

By the way, if I used %matplotlib agg and %matplotlib inline instead of matplotlib.use('agg') and matplotlib.use('inline'), the switching of backends didn't cause any problems.

I attached a screenshot of demo codes for reproducing the problem.