René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"[Bug]: manual positioning fails for ax.clabel","articleBody":"### Bug summary\n\nWhen adding the label position with the `manual` keyword, an `IndexError` is raised when using fewer levels than available in the contour.\n\n### Code for reproduction\n\n```Python\n# create random data\nfrom matplotlib import pyplot as plt\nimport numpy as np\nfig, ax = plt.subplots()\nlen_data = 10000\nxs = np.random.normal(0, 1, len_data)\nys = np.random.normal(0, 1, len_data)\nhist, x_edges, y_edges = np.histogram2d(xs, ys, bins=20)\nXc = 0.5 * (x_edges[:-1] + x_edges[1:])\nYc = 0.5 * (y_edges[:-1] + y_edges[1:])\nflat = hist.flatten()\norder = np.argsort(flat)[::-1]\ncumsum = np.cumsum(flat[order])\ncumsum/=cumsum[-1]\n\n# compute contour levels\nprob_levels = [0.95, 0.5]\nclevels=[flat[order][np.searchsorted(cumsum, p)] for p in prob_levels]\n\n#plot contour\ncontour = ax.contour(Xc, Yc, hist.T,levels = clevels)\nax.clabel(contour, levels= [clevels[-1]], fmt = {clevels[-1]: 'Label'},  inline=True, fontsize=ax.xaxis.label.get_size(), manual = [(1, 0.5)])\n\nplt.show()\n```\n\n### Actual outcome\n\nline 22, in \u003cmodule\u003e\n    ax.clabel(contour, levels= [clevels[-1]], fmt = {clevels[-1]: 'Label'},  inline=True, fontsize=ax.xaxis.label.get_size(), manual = [(1, 0.5)])\n  File \"/home/.conda/envs/test_env/lib/python3.12/site-packages/matplotlib/axes/_axes.py\", line 6697, in clabel\n    return CS.clabel(levels, **kwargs)\n           ^^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"/home/.conda/envs/test_env/lib/python3.12/site-packages/matplotlib/contour.py\", line 195, in clabel\n    self.add_label_near(x, y, inline, inline_spacing)\n  File \"/home/.conda/envs/test_env/lib/python3.12/site-packages/matplotlib/contour.py\", line 562, in add_label_near\n    self.add_label(*proj, rotation, self.labelLevelList[idx_level_min],\n                                    ~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^\nIndexError: list index out of range\n\n\n### Expected outcome\n\nA contour label should be created only on the inner `contour```\n\n### Additional information\n\nThis seems to be due to [this line](https://github.com/matplotlib/matplotlib/blob/dd8d78b8dce60b6c8db86132892577a0b9dbe469/lib/matplotlib/contour.py#L460), where `\n        self.add_label(*proj, rotation, self.labelLevelList[idx_level_min],\n                       self.labelCValueList[idx_level_min])`\nshould rather be `\n        self.add_label(*proj, rotation, self.labelLevelList[level],\n                       self.labelCValueList[level])`\n\n### Operating system\n\nUbuntu\n\n### Matplotlib Version\n\n3.10.6\n\n### Matplotlib Backend\n\n_No response_\n\n### Python version\n\n3.12\n\n### Jupyter version\n\n_No response_\n\n### Installation\n\nNone","author":{"url":"https://github.com/Hen42rik","@type":"Person","name":"Hen42rik"},"datePublished":"2026-05-18T16:14:00.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":3},"url":"https://github.com/31702/matplotlib/issues/31702"}