René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"`stairs` with dashed linestyle and fill=True raises ValueError","articleBody":"If you change `test_stairs_options` to `mpl20` style, then it crashes. What we have worked out is that it is due to artist \"G\", which sets `ls='--', fill=True`, but does _not_ set a `linewidth`.\n\nThe setup for `stairs` sets a default `linewidth=0` if `fill=True`. The difference between classic and mpl20 styles is that the latter performs `linewidth`-scaling on the `linestyle`. So in mpl20 style, the dashes are scaled to 0, which raises in the backend.\n\n\u003e ```\n\u003e __________________ test_stairs_options[png] ___________________\n\u003e \n\u003e args = (), kwds = {'extension': 'png', 'request': \u003cFixtureRequest for \u003cFunction test_stairs_options[png]\u003e\u003e}\n\u003e \n\u003e     @wraps(func)\n\u003e     def inner(*args, **kwds):\n\u003e         with self._recreate_cm():\n\u003e           return func(*args, **kwds)\n\u003e \n\u003e /usr/lib64/python3.13/contextlib.py:85: \n\u003e  _ _ _ _ _ _ _ _ _ _ _ _\n\u003e lib/matplotlib/figure.py:3508: in savefig\n\u003e     self.canvas.print_figure(fname, **kwargs)\n\u003e lib/matplotlib/backend_bases.py:2275: in print_figure\n\u003e     result = print_method(\n\u003e lib/matplotlib/backend_bases.py:2132: in \u003clambda\u003e\n\u003e     print_method = functools.wraps(meth)(lambda *args, **kwargs: meth(\n\u003e lib/matplotlib/backends/backend_agg.py:539: in print_png\n\u003e     self._print_pil(filename_or_obj, \"png\", pil_kwargs, metadata)\n\u003e lib/matplotlib/backends/backend_agg.py:487: in _print_pil\n\u003e     FigureCanvasAgg.draw(self)\n\u003e lib/matplotlib/backends/backend_agg.py:440: in draw\n\u003e     self.figure.draw(self.renderer)\n\u003e lib/matplotlib/artist.py:94: in draw_wrapper\n\u003e     result = draw(artist, renderer, *args, **kwargs)\n\u003e lib/matplotlib/artist.py:71: in draw_wrapper\n\u003e     return draw(artist, renderer)\n\u003e lib/matplotlib/figure.py:3275: in draw\n\u003e     mimage._draw_list_compositing_images(\n\u003e lib/matplotlib/image.py:133: in _draw_list_compositing_images\n\u003e     a.draw(renderer)\n\u003e lib/matplotlib/artist.py:71: in draw_wrapper\n\u003e     return draw(artist, renderer)\n\u003e lib/matplotlib/axes/_base.py:3282: in draw\n\u003e     mimage._draw_list_compositing_images(\n\u003e lib/matplotlib/image.py:133: in _draw_list_compositing_images\n\u003e     a.draw(renderer)\n\u003e lib/matplotlib/artist.py:71: in draw_wrapper\n\u003e     return draw(artist, renderer)\n\u003e lib/matplotlib/patches.py:740: in draw\n\u003e     self._draw_paths_with_artist_properties(\n\u003e lib/matplotlib/patches.py:723: in _draw_paths_with_artist_properties\n\u003e     gc.set_dashes(*self._dash_pattern)\n\u003e _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _\n\u003e \n\u003e self = \u003cmatplotlib.backend_bases.GraphicsContextBase object at 0x7f3016ba3750\u003e, dash_offset = 0.0, dash_list = [0.0, 0.0]\n\u003e \n\u003e     def set_dashes(self, dash_offset, dash_list):\n\u003e         \"\"\"\n\u003e         Set the dash style for the gc.\n\u003e     \n\u003e         Parameters\n\u003e         ----------\n\u003e         dash_offset : float\n\u003e             Distance, in points, into the dash pattern at which to\n\u003e             start the pattern. It is usually set to 0.\n\u003e         dash_list : array-like or None\n\u003e             The on-off sequence as points.  None specifies a solid line. All\n\u003e             values must otherwise be non-negative (:math:`\\\\ge 0`).\n\u003e     \n\u003e         Notes\n\u003e         -----\n\u003e         See p. 666 of the PostScript\n\u003e         `Language Reference\n\u003e         \u003chttps://www.adobe.com/jp/print/postscript/pdfs/PLRM.pdf\u003e`_\n\u003e         for more info.\n\u003e         \"\"\"\n\u003e         if dash_list is not None:\n\u003e             dl = np.asarray(dash_list)\n\u003e             if np.any(dl \u003c 0.0):\n\u003e                 raise ValueError(\n\u003e                     \"All values in the dash list must be non-negative\")\n\u003e             if dl.size and not np.any(dl \u003e 0.0):\n\u003e               raise ValueError(\n\u003e                     'At least one value in the dash list must be positive')\n\u003e E               ValueError: At least one value in the dash list must be positive\n\u003e \n\u003e lib/matplotlib/backend_bases.py:897: ValueError\n\u003e ``` \n\n _Originally posted by @QuLogic in [#31300](https://github.com/matplotlib/matplotlib/pull/31300/changes/d1d3d894a39e79b6d740a6586909714cd68fc3ef#r2932743766)_","author":{"url":"https://github.com/QuLogic","@type":"Person","name":"QuLogic"},"datePublished":"2026-03-13T20:02:21.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":5},"url":"https://github.com/31302/matplotlib/issues/31302"}