Bug report

Bug summary

Using ipywidgets.interact to update a figure works as expected in matplotlib<=3.3.1, but fails in matplotlib==3.3.2.

I don't think this is an ipywidgets issue since downgrading matplotlib fixes this issue.

Code for reproduction

In[1]:

%matplotlib notebook
import matplotlib as mpl
import matplotlib.pyplot as plt
import ipywidgets as ipyw
"works if %s <= 3.3.1" % mpl.__version__

In[2]:

fig = plt.figure()
@ipyw.interact(m=ipyw.FloatSlider(value=1, min=-10, max=10, step=0.01))
def update(m):
    plt.figure(fig.number, clear=True)
    plt.plot([m * x for x in range(-9, 10)])

Followed by moving the slider.

Actual outcome

• when moving the slider, the figure does not update
• a second figure is sometimes created instead
• the second figure is usually blank, but sometimes updates instead

Expected outcome

• the original figure updates as it does in matplotlib==3.3.1

Matplotlib version

• Operating system: Ubuntu
• Matplotlib version: 3.3.2 vs 3.3.1
• Matplotlib backend (print(matplotlib.get_backend())): nbAgg
• Python version: 3.7.8
• Jupyter version (if applicable): jupyter-core==4.6.3
• Other libraries: ipywidgets==7.5.1
• Installation source: conda channel conda-forge