[Bug]: ValueError thrown when levels is set to a lower value than vmin when using contours method of Axes
#26531
Comments
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This appears to be related to #25247, which changed the inheritance of the In this case, it is not actually a fatal error, as far as I can tell... when I run it it continues after printing the traceback. The problem is that it is doing checks at every step, so Essentially it is first autoscalling, then applying the vmin/vmax that were specified, so it goes: This pattern of This can be suppressed (on our end) by doing: diff --git a/lib/matplotlib/contour.py b/lib/matplotlib/contour.py
index 79f66b8961..ab88faf28c 100644
--- a/lib/matplotlib/contour.py
+++ b/lib/matplotlib/contour.py
@@ -887,11 +887,12 @@ class ContourSet(ContourLabeler, mcoll.Collection):
self.set_cmap(cmap)
if norm is not None:
self.set_norm(norm)
- if vmin is not None:
- self.norm.vmin = vmin
- if vmax is not None:
- self.norm.vmax = vmax
- self._process_colors()
+ with self.norm.callbacks.blocked(signal="changed"):
+ if vmin is not None:
+ self.norm.vmin = vmin
+ if vmax is not None:
+ self.norm.vmax = vmax
+ self._process_colors()
if self._paths is None:
self._paths = self._make_paths_from_contour_generator()But perhaps there are more areas where such supression needs to happen? Or perhaps @anntzer thoughts? |
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A better fix is likely possible, but your patch seems correct at first glance. |
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(As a side point, perhaps there should be a helper method that lets one set both vmin and vmax on a norm and only trigger the validation and signals once both have been set -- in essence wrapping the patch written by @ksunden) |
Bug summary
With the recent mpl prerelease, we started to have a failure in the test suite of nilearn, a package that depends on matplotlib for visualization. I reproduced the error with a matplotlib example and it seems that when calling
Axes.contoursit's not possible to set thelevelsparameter to values less thanvminusing array-like input. This happens even whenvmaxis also set by the user and it seems to be because vmax ends up being set to 0 internally. The code reproduced below will throwValueError: minvalue must be less than or equal to maxvalue. I'm not sure if it's a usage error or a bug so let me know if this is expected behavior, however as I understand it the values forlevelsandvminandvmaxshould be independent.Code for reproduction
Actual outcome
Expected outcome
A plot matplotlib.contour.QuadContourSet object
Additional information
The test that led to this failure did pass before this version
Operating system
Ubuntu 22.04
Matplotlib Version
3.8.0rc1
Matplotlib Backend
module://matplotlib_inline.backend_inline
Python version
3.10.4
Jupyter version
No response
Installation
pip
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