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3.5.0b1: ax.contour generates different artists #20906
Description
Bug summary
The artists added when using ax.contour have changed abruptly from 3.4 to the 3.5 beta. This causes issues for workflows that use the artist properties.
Code for reproduction
import numpy as np
import matplotlib.pyplot as plt
xx, yy = np.mgrid[-3:3:.01, 0:1:.05]
zz = np.sin(xx * yy)
ax = plt.figure().subplots()
ax.contour(xx, yy, zz)
print(ax.collections[0].__class__)Actual outcome
The result on 3.5.0b1:
<class 'matplotlib.collections.PathCollection'>Expected outcome
The result on 3.4.1:
<class 'matplotlib.collections.LineCollection'>
Activity
tacaswell commentedon Aug 25, 2021
@mwaskom What are you doing with the return of
get_segments? I am 👎🏻 on backing out these changes, but we need a better mitigation / migration story for the people we have broken.attn @ianthomas23
mwaskom commentedon Aug 25, 2021
In seaborn, just accessing them to test the 2D kdeplot results.
Like #20895, I don't think this affects any user-facing code, so it's not especially critical for me.
But since my test suite turned up an unexpected breakage, I thought it was good to report anyway.
ianthomas23 commentedon Aug 26, 2021
@mwaskom The change in class returned by
contourfromLineCollectiontoPathCollectionis intended. The PR (#19623) fixes a bug that has been around for many years in that closed line loops were rendered as open line strips so the ends were not joined correctly. To fix this it was necessary internally to use theCLOSEPOLYPath code.LineCollectiondoesn't support the use of codes whereasPathCollectiondoes, hence the change.There should certainly have been a note about the API change. If someone else wants to pick this up that would be great - I am on holiday at the moment and start a new job next week so mpl is not my highest priority in the short term.
mwaskom commentedon Aug 26, 2021
I appreciate that it was intentional. FWIW, forward guidance on such changes a version or so in advance (either just in release notes, or ideally with a future warning) would reduce the change of abrupt breakage.
Document API change in ContourSet
Document API change in ContourSet
Document API change in ContourSet
timhoffm commentedon Sep 30, 2021
Is @QuLogic ‘s documentation enough to close this issue?
Document API change in ContourSet
Document API change in ContourSet