Bug summary
I am running into issues with removing contour lines with Matplotlib 3.5.0rc1 - this worked with previous stable versions of Matplotlib, so it is a regression. I think this started failing with #19623.
The bug is triggered when contour lines are added and removed inside an artist. The example code below may appear a little convoluted, but it represents how the contours are drawn in WCSAxes, and the error happens the second time the figure is saved (once the contours have been removed and re-added).
Using objgraph reveals that after the contour lines are removed from the plot, there are residual references to the original PathCollection objects which are causing them to be drawn, but since .figure is no longer set on them, the code crashes.
Code for reproduction
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.artist import Artist
class WCSAxesArtist(Artist):
def draw(self, renderer, *args, **kwargs):
if hasattr(self, '_cset') and self._cset:
for line in self._cset.collections:
line.remove()
self._cset = self.axes.contour(np.arange(100).reshape(10, 10), levels=[50])
fig = plt.figure()
ax = fig.add_subplot(1, 1, 1)
artist = WCSAxesArtist()
ax.add_artist(artist)
plt.savefig('test.png')
plt.savefig('test.png')Actual outcome
An error occurs the second time the figure is saved:
Traceback (most recent call last):
File "/Users/tom/Dropbox/Code/Astropy/astropy/debug.py", line 19, in <module>
plt.savefig('test.png')
File "/Users/tom/python/dev/lib/python3.9/site-packages/matplotlib/pyplot.py", line 958, in savefig
res = fig.savefig(*args, **kwargs)
File "/Users/tom/python/dev/lib/python3.9/site-packages/matplotlib/figure.py", line 3012, in savefig
self.canvas.print_figure(fname, **kwargs)
File "/Users/tom/python/dev/lib/python3.9/site-packages/matplotlib/backend_bases.py", line 2309, in print_figure
result = print_method(
File "/Users/tom/python/dev/lib/python3.9/site-packages/matplotlib/backend_bases.py", line 1643, in wrapper
return func(*args, **kwargs)
File "/Users/tom/python/dev/lib/python3.9/site-packages/matplotlib/_api/deprecation.py", line 412, in wrapper
return func(*inner_args, **inner_kwargs)
File "/Users/tom/python/dev/lib/python3.9/site-packages/matplotlib/backends/backend_agg.py", line 538, in print_png
FigureCanvasAgg.draw(self)
File "/Users/tom/python/dev/lib/python3.9/site-packages/matplotlib/backends/backend_agg.py", line 434, in draw
self.figure.draw(self.renderer)
File "/Users/tom/python/dev/lib/python3.9/site-packages/matplotlib/artist.py", line 73, in draw_wrapper
result = draw(artist, renderer, *args, **kwargs)
File "/Users/tom/python/dev/lib/python3.9/site-packages/matplotlib/artist.py", line 50, in draw_wrapper
return draw(artist, renderer)
File "/Users/tom/python/dev/lib/python3.9/site-packages/matplotlib/figure.py", line 2803, in draw
mimage._draw_list_compositing_images(
File "/Users/tom/python/dev/lib/python3.9/site-packages/matplotlib/image.py", line 132, in _draw_list_compositing_images
a.draw(renderer)
File "/Users/tom/python/dev/lib/python3.9/site-packages/matplotlib/artist.py", line 50, in draw_wrapper
return draw(artist, renderer)
File "/Users/tom/python/dev/lib/python3.9/site-packages/matplotlib/axes/_base.py", line 3082, in draw
mimage._draw_list_compositing_images(
File "/Users/tom/python/dev/lib/python3.9/site-packages/matplotlib/image.py", line 132, in _draw_list_compositing_images
a.draw(renderer)
File "/Users/tom/python/dev/lib/python3.9/site-packages/matplotlib/artist.py", line 50, in draw_wrapper
return draw(artist, renderer)
File "/Users/tom/python/dev/lib/python3.9/site-packages/matplotlib/collections.py", line 976, in draw
self.set_sizes(self._sizes, self.figure.dpi)
AttributeError: 'NoneType' object has no attribute 'dpi'
Expected outcome
No console output
Operating system
MacOS X
Matplotlib Version
3.5.0rc1
Matplotlib Backend
Agg
Python version
3.9.7
Jupyter version
No response
Other libraries
No response
Installation
pip
Conda channel
No response
Bug summary
I am running into issues with removing contour lines with Matplotlib 3.5.0rc1 - this worked with previous stable versions of Matplotlib, so it is a regression. I think this started failing with #19623.
The bug is triggered when contour lines are added and removed inside an artist. The example code below may appear a little convoluted, but it represents how the contours are drawn in WCSAxes, and the error happens the second time the figure is saved (once the contours have been removed and re-added).
Using objgraph reveals that after the contour lines are removed from the plot, there are residual references to the original PathCollection objects which are causing them to be drawn, but since
.figureis no longer set on them, the code crashes.Code for reproduction
Actual outcome
An error occurs the second time the figure is saved:
Expected outcome
No console output
Operating system
MacOS X
Matplotlib Version
3.5.0rc1
Matplotlib Backend
Agg
Python version
3.9.7
Jupyter version
No response
Other libraries
No response
Installation
pip
Conda channel
No response