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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"[Bug]: Crash when removing colorbar axes in a constrained layout","articleBody":"### Bug summary\n\nThe program crashes if we remove the axes of the colorbar `cbar` by calling `cbar.ax.remove()` in a figure with constrained layout. The crash does not occur if we do not specify a constrained layout.\n\n### Code for reproduction\n\n```Python\nimport matplotlib.pyplot as plt\nimport numpy as np\n\ndelta = 0.025\nx = y = np.arange(-3.0, 3.01, delta)\nX, Y = np.meshgrid(x, y)\nZ1 = np.exp(-X**2 - Y**2)\nZ2 = np.exp(-(X - 1)**2 - (Y - 1)**2)\nZ = (Z1 - Z2) * 2\n\nfig, ax = plt.subplots(layout='constrained')\nCS = ax.contourf(X, Y, Z, 10, cmap=\"bone\")\ncbar = fig.colorbar(CS)\ncbar.ax.remove()\nplt.show()\n```\n\n### Actual outcome\n\n---------------------------------------------------------------------------\nAttributeError                            Traceback (most recent call last)\nFile ~/anaconda3/lib/python3.11/site-packages/matplotlib/backend_bases.py:1152, in TimerBase._on_timer(self)\n   1146 \"\"\"\n   1147 Runs all function that have been registered as callbacks. Functions\n   1148 can return False (or 0) if they should not be called any more. If there\n   1149 are no callbacks, the timer is automatically stopped.\n   1150 \"\"\"\n   1151 for func, args, kwargs in self.callbacks:\n-\u003e 1152     ret = func(*args, **kwargs)\n   1153     # docstring above explains why we use `if ret == 0` here,\n   1154     # instead of `if not ret`.\n   1155     # This will also catch `ret == False` as `False == 0`\n   1156     # but does not annoy the linters\n   1157     # https://docs.python.org/3/library/stdtypes.html#boolean-values\n   1158     if ret == 0:\n\nFile ~/anaconda3/lib/python3.11/site-packages/matplotlib/backends/backend_macosx.py:71, in FigureCanvasMac._single_shot_timer.\u003clocals\u003e.callback_func(callback, timer)\n     70 def callback_func(callback, timer):\n---\u003e 71     callback()\n     72     self._timers.remove(timer)\n\nFile ~/anaconda3/lib/python3.11/site-packages/matplotlib/backends/backend_macosx.py:93, in FigureCanvasMac._draw_idle(self)\n     91     return\n     92 self._draw_pending = False\n---\u003e 93 self.draw()\n\nFile ~/anaconda3/lib/python3.11/site-packages/matplotlib/backends/backend_macosx.py:56, in FigureCanvasMac.draw(self)\n     54     return\n     55 with cbook._setattr_cm(self, _is_drawing=True):\n---\u003e 56     super().draw()\n     57 self.update()\n\nFile ~/anaconda3/lib/python3.11/site-packages/matplotlib/backends/backend_agg.py:382, in FigureCanvasAgg.draw(self)\n    379 # Acquire a lock on the shared font cache.\n    380 with (self.toolbar._wait_cursor_for_draw_cm() if self.toolbar\n    381       else nullcontext()):\n--\u003e 382     self.figure.draw(self.renderer)\n    383     # A GUI class may be need to update a window using this draw, so\n    384     # don't forget to call the superclass.\n    385     super().draw()\n\nFile ~/anaconda3/lib/python3.11/site-packages/matplotlib/artist.py:94, in _finalize_rasterization.\u003clocals\u003e.draw_wrapper(artist, renderer, *args, **kwargs)\n     92 @wraps(draw)\n     93 def draw_wrapper(artist, renderer, *args, **kwargs):\n---\u003e 94     result = draw(artist, renderer, *args, **kwargs)\n     95     if renderer._rasterizing:\n     96         renderer.stop_rasterizing()\n\nFile ~/anaconda3/lib/python3.11/site-packages/matplotlib/artist.py:71, in allow_rasterization.\u003clocals\u003e.draw_wrapper(artist, renderer)\n     68     if artist.get_agg_filter() is not None:\n     69         renderer.start_filter()\n---\u003e 71     return draw(artist, renderer)\n     72 finally:\n     73     if artist.get_agg_filter() is not None:\n\nFile ~/anaconda3/lib/python3.11/site-packages/matplotlib/figure.py:3251, in Figure.draw(self, renderer)\n   3249 if self.axes and self.get_layout_engine() is not None:\n   3250     try:\n-\u003e 3251         self.get_layout_engine().execute(self)\n   3252     except ValueError:\n   3253         pass\n\nFile ~/anaconda3/lib/python3.11/site-packages/matplotlib/layout_engine.py:278, in ConstrainedLayoutEngine.execute(self, fig)\n    275 w_pad = self._params['w_pad'] / width\n    276 h_pad = self._params['h_pad'] / height\n--\u003e 278 return do_constrained_layout(fig, w_pad=w_pad, h_pad=h_pad,\n    279                              wspace=self._params['wspace'],\n    280                              hspace=self._params['hspace'],\n    281                              rect=self._params['rect'],\n    282                              compress=self._compress)\n\nFile ~/anaconda3/lib/python3.11/site-packages/matplotlib/_constrained_layout.py:116, in do_constrained_layout(fig, h_pad, w_pad, hspace, wspace, rect, compress)\n    106     return\n    108 for _ in range(2):\n    109     # do the algorithm twice.  This has to be done because decorations\n    110     # change size after the first re-position (i.e. x/yticklabels get\n   (...)\n    114     # make margins for all the Axes and subfigures in the\n    115     # figure.  Add margins for colorbars...\n--\u003e 116     make_layout_margins(layoutgrids, fig, renderer, h_pad=h_pad,\n    117                         w_pad=w_pad, hspace=hspace, wspace=wspace)\n    118     make_margin_suptitles(layoutgrids, fig, renderer, h_pad=h_pad,\n    119                           w_pad=w_pad)\n    121     # if a layout is such that a columns (or rows) margin has no\n    122     # constraints, we need to make all such instances in the grid\n    123     # match in margin size.\n\nFile ~/anaconda3/lib/python3.11/site-packages/matplotlib/_constrained_layout.py:405, in make_layout_margins(layoutgrids, fig, renderer, w_pad, h_pad, hspace, wspace)\n    403 cbp_rspan, cbp_cspan = get_cb_parent_spans(cbax)\n    404 loc = cbax._colorbar_info['location']\n--\u003e 405 cbpos, cbbbox = get_pos_and_bbox(cbax, renderer)\n    406 if loc == 'right':\n    407     if cbp_cspan.stop == ss.colspan.stop:\n    408         # only increase if the colorbar is on the right edge\n\nFile ~/anaconda3/lib/python3.11/site-packages/matplotlib/_constrained_layout.py:644, in get_pos_and_bbox(ax, renderer)\n    642 pos = ax.get_position(original=True)\n    643 # pos is in panel co-ords, but we need in figure for the layout\n--\u003e 644 pos = pos.transformed(fig.transSubfigure - fig.transFigure)\n    645 tightbbox = martist._get_tightbbox_for_layout_only(ax, renderer)\n    646 if tightbbox is None:\n\nAttributeError: 'NoneType' object has no attribute 'transSubfigure'\n\n\n### Expected outcome\n\nA plot without the colorbar is displayed without errors.\n\n### Additional information\n\n_No response_\n\n### Operating system\n\n_No response_\n\n### Matplotlib Version\n\n0.2.0.dev53882+unknown.g607d2c380.g02b42db27\n\n### Matplotlib Backend\n\n_No response_\n\n### Python version\n\n_No response_\n\n### Jupyter version\n\n_No response_\n\n### Installation\n\nNone","author":{"url":"https://github.com/williamlus","@type":"Person","name":"williamlus"},"datePublished":"2026-03-19T04:44:52.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/31330/matplotlib/issues/31330"}