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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"[Bug]: twinx() and twiny() crash with cryptic errors on 3D axes","articleBody":"# [Bug]: twinx() and twiny() crash with cryptic errors on 3D axes\n\n## Bug summary\nCalling `twinx()` or `twiny()` on a 3D axes object raises cryptic internal\nerrors with no user-friendly message. Both methods are inherited from the base\nAxes class but are incompatible with Axes3D, and no guard or clear error\nexists to tell the user this.\n\n- `ax3d.twinx()` → AttributeError: 'YAxis' object has no attribute 'tick_left'  \n- `ax3d.twiny()` → ValueError: 'bottom' is not a valid value for position; supported values are 'lower', 'upper', 'both', 'default', 'none'  \n\nBoth errors originate deep inside internal axis machinery, giving the user no\nindication that the operation is simply unsupported on 3D axes.\n\n---\n\n## Code for reproduction\n\n```python\nimport matplotlib.pyplot as plt\n\n# twinx() on 3D axes\nfig = plt.figure()\nax = fig.add_subplot(111, projection='3d')\nax.scatter([1, 2, 3], [1, 2, 3], [1, 2, 3])\nax2 = ax.twinx()   # AttributeError\nplt.show()\n```\n\n```python\nimport matplotlib.pyplot as plt\n\n# twiny() on 3D axes\nfig = plt.figure()\nax = fig.add_subplot(111, projection='3d')\nax.scatter([1, 2, 3], [1, 2, 3], [1, 2, 3])\nax2 = ax.twiny()   # ValueError\nplt.show()\n```\n\n---\n\n## Actual outcome\n\n### twinx()\n```\nTraceback (most recent call last):\n  File \"repro.py\", line 6, in \u003cmodule\u003e\n    ax2 = ax.twinx()\n  File \".../matplotlib/axes/_base.py\", line 4642, in twinx\n    self.yaxis.tick_left()\n    ^^^^^^^^^^^^^^^^^^^^\nAttributeError: 'YAxis' object has no attribute 'tick_left'\n```\n\n### twiny()\n```\nTraceback (most recent call last):\n  File \"repro.py\", line 6, in \u003cmodule\u003e\n    ax2 = ax.twiny()\n  File \".../matplotlib/axes/_base.py\", line 4662, in twiny\n    self.xaxis.tick_bottom()\n    ^^^^^^^^^^^^^^^^^^^^^^^^\nValueError: 'bottom' is not a valid value for position; supported values\nare 'lower', 'upper', 'both', 'default', 'none'\n```\n\n---\n\n## Expected outcome\nA clear, early NotImplementedError (or TypeError) that tells the user\n`twinx()/twiny()` is not supported on 3D axes. For example:\n\n```\nNotImplementedError: twinx() is not supported on 3D axes (Axes3D).\nUse a separate 2D axes if you need a twin axis.\n```\n\nThis is consistent with how other methods guard against misuse on\nnon-2D projections.\n\n---\n\n## Root cause\nAxes3D inherits `twinx()` and `twiny()` from `_AxesBase` without\noverriding them. Inside `twinx()`, the first thing that happens is:\n\n```python\n# lib/matplotlib/axes/_base.py\ndef twinx(self):\n    ...\n    self.yaxis.tick_left()   # \u003c-- 3D YAxis has no tick_left()\n```\n\nThe 3D YAxis subclass does not implement `tick_left()` or `tick_right()`\nbecause those concepts don't map to a 3D axis. The fix is to add an early\noverride in Axes3D:\n\n```python\n# lib/mpl_toolkits/mplot3d/axes3d.py\ndef twinx(self):\n    raise NotImplementedError(\n        \"twinx() is not supported on 3D axes. \"\n        \"Use a separate 2D Axes for a twin axis.\"\n    )\n\ndef twiny(self):\n    raise NotImplementedError(\n        \"twiny() is not supported on 3D axes. \"\n        \"Use a separate 2D Axes for a twin axis.\"\n    )\n```\n\n---\n\n## Reproducibility\nFails on every call, with any data, regardless of whether the 3D\naxes has been plotted to or not:\n\n- Empty 3D axes  \n  → AttributeError: 'YAxis' object has no attribute 'tick_left'  \n\n- 3D axes with scatter data  \n  → Same  \n\n- 3D axes with plot data  \n  → Same  \n\n- twiny() variant  \n  → ValueError: 'bottom' is not a valid value for position  \n\n---\n\n## Additional information\nAlso broken on polar axes (different error):\n\n```python\nfig, ax = plt.subplots(subplot_kw={'projection': 'polar'})\nax.twinx()\n```\n\n```\nValueError: Cannot set Axes adjustable to 'datalim' for Axes which\noverride 'get_data_ratio'\n```\n\nAll three non-2D projection types (3d, polar) give different, cryptic\nerrors for the same unsupported operation. A consistent\nNotImplementedError with a helpful message would benefit all of them.\n\n---\n\n## Environment\n- Operating system: Linux (Ubuntu 24.04)  \n- Matplotlib version: 3.10.8  \n- Python version: 3.12.3  \n- Installation: pip  ","author":{"url":"https://github.com/buddy0452004","@type":"Person","name":"buddy0452004"},"datePublished":"2026-04-18T06:51:43.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/31523/matplotlib/issues/31523"}