matplotlib / matplotlib/matplotlib
[Bug]: Contour segments changed after clabel
Nobody has claimed this yet.
- Dominant language
- Python
- Stars
- 23.2k
- Forks
- 8.5k
- Avg merge
- 1d 6h
- Merged PRs (30d)
- 66
Description
### Bug summary
`ax.clabel` changes the contour segments itself as it removes the label part of the contours.
Python 3.11.8 + Matplotlib 3.7.1 doesn't change the contour itself, where as Python 3.11.9 + Matplotlib 3.9.1 changes it. Is this an intended change?
### Code for reproduction
```Python
import numpy as np
import matplotlib.pyplot as plt
size = 1000
sigma_x = 1.
sigma_y = 1.
x = np.linspace(-3, 3, size)
y = np.linspace(-3, 3, size)
xx, yy = np.meshgrid(x, y)
z = (1/(2*np.pi*sigma_x*sigma_y) * np.exp(-(xx**2/(2*sigma_x**2)
+ yy**2/(2*sigma_y**2))))
extent = [x[0], x[-1], y[0], y[-1]]
fig, ax = plt.subplots()
ax.imshow(z, extent=extent)
cs = ax.contour(z, extent=extent, colors='w')
seg1 = cs.allsegs[3][0]
ax.clabel(cs, cs.levels, fmt='%.5f%%', fontsize=15)
seg2 = cs.allsegs[3][0]
plt.show()
fig, (ax1, ax2) = plt.subplots(1, 2, figsize=(6, 3))
ax1.plot(seg1[:, 0], seg1[:, 1], marker='.', ms=1)
ax1.set_title('Before ax.clabel')
ax2.plot(seg2[:, 0], seg2[:, 1], marker='.', ms=1)
ax2.set_title('After ax.clabel')
plt.show()
```
### Actual outcome
Contour segments changed after `ax.clabel`. The labeled part is removed from the contour
### Expected outcome
Keep the contour segment unchanged
### Additional information
Python 3.11.8 + Matplotlib 3.7.1 doesn't change the contour itself, where as Python 3.11.9 + Matplotlib 3.9.1 changes it. Is this an intended change?
### Operating system
MacOS
### Matplotlib Version
3.9.1
### Matplotlib Backend
_No response_
### Python version
3.11.9
### Jupyter version
_No response_
### Installation
None
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with the provided Python reproduction and the ax.clabel entry point, comparing Matplotlib 3.7.1 and 3.9.1 behavior. Inspect how contour segments are represented before and after labeling. Done means determining whether the changed segments are intentional and, if not, preserving the original contour segment while still displaying the label.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- data-visualization
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100