Repository navigation
[Bug]: violin's default alpha no longer persists #30613
Description
Bug summary
Perhaps this is an understood and accepted behaviour change, but I did not see anything in the changenotes. If we set the facecolor of a violin object after creating it, we now also override the default alpha.
Code for reproduction
import matplotlib.pyplot as plt
import numpy as np
fig, ax = plt.subplots()
data = np.random.normal(size=(10, 3))
violins = ax.violinplot(data)
first_violin = violins['bodies'][0]
first_violin.set_facecolor('tab:red')
plt.show()Actual outcome
With main I get
Expected outcome
With 3.10 I get
Additional information
Bisects to #27304. The default alpha is now included in the default facecolor as a (color, alpha) tuple, rather than being passed by the alpha parameter.
Operating system
Ubuntu
Matplotlib Version
main
Matplotlib Backend
qtagg
Python version
3.13.7
Jupyter version
No response
Installation
git checkout
Activity
timhoffm commentedon Sep 29, 2025
Oh, this extra tracking of alpha is a nuissance.
It's tricky to maintain the behavior. Previously, we had
facecolor=c, alpha=0.3. We have moved the default alpha into facecolor, because the explicit parameter would overwrite any alpha in user-defined colors. So the only two options are the present change of behavior or you distinguish and setalpha=0.3only when there are no user-defined colors.Without context, I would be inclined to accept the breakage to keep the logic simple. But OTOH your example was the standard way to color violins before, so it is not acceptable to break that.
Thanks for finding out!
FIX: Keep legacy alpha behavior for violinplot without facecolor
FIX: Keep legacy alpha behavior for violinplot without facecolor
FIX: Keep legacy alpha behavior for violinplot without facecolor