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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"[Bug]: Different behaviour between showing and savefig PDF","articleBody":"### Bug summary\n\nHi there, \nI came across an error that was tricky to debug, as it had some unexpected behaviour. Basically, I used ls=\"\" in a scatter plot, which rise an issue if i understand it correctly. But when plt.show(), the image is displayed perfectly, while plt.savefig for PDF specifically crashes with the unreadable error below (`ValueError: zero-size array to reduction operation maximum which has no identity`).\n\nYou can find the minimum example below. Please uncomment plt.show() for no error.\n\n### Code for reproduction\n\n```Python\nplt.figure()\nplt.scatter([0, 1], [0, 1], ls=\"\")\n#plt.show()\nplt.savefig(\"test.pdf\")\n```\n\n### Actual outcome\n\n```\nTraceback (most recent call last):\n  File \"\u003cuser_script\u003e.py\", line \u003cline_number\u003e, in \u003cmodule\u003e\n    \u003cuser_function\u003e()\n  File \"\u003cuser_script\u003e.py\", line \u003cline_number\u003e, in \u003cuser_function\u003e\n    plt.savefig(\"\u003coutput_file\u003e.pdf\")\n  File \"\u003cpython_env\u003e/lib/python3.11/site-packages/matplotlib/pyplot.py\", line 1228, in savefig\n    res = fig.savefig(*args, **kwargs)\n          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"\u003cpython_env\u003e/lib/python3.11/site-packages/matplotlib/figure.py\", line 3395, in savefig\n    self.canvas.print_figure(fname, **kwargs)\n  File \"\u003cpython_env\u003e/lib/python3.11/site-packages/matplotlib/backend_bases.py\", line 2204, in print_figure\n    result = print_method(\n             ^^^^^^^^^^^^^\n  File \"\u003cpython_env\u003e/lib/python3.11/site-packages/matplotlib/backend_bases.py\", line 2054, in \u003clambda\u003e\n    print_method = functools.wraps(meth)(lambda *args, **kwargs: meth(\n                                                                 ^^^^^\n  File \"\u003cpython_env\u003e/lib/python3.11/site-packages/matplotlib/backends/backend_pdf.py\", line 2799, in print_pdf\n    self.figure.draw(renderer)\n  File \"\u003cpython_env\u003e/lib/python3.11/site-packages/matplotlib/artist.py\", line 95, in draw_wrapper\n    result = draw(artist, renderer, *args, **kwargs)\n             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"\u003cpython_env\u003e/lib/python3.11/site-packages/matplotlib/artist.py\", line 72, in draw_wrapper\n    return draw(artist, renderer)\n           ^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"\u003cpython_env\u003e/lib/python3.11/site-packages/matplotlib/figure.py\", line 3162, in draw\n    mimage._draw_list_compositing_images(\n  File \"\u003cpython_env\u003e/lib/python3.11/site-packages/matplotlib/image.py\", line 132, in _draw_list_compositing_images\n    a.draw(renderer)\n  File \"\u003cpython_env\u003e/lib/python3.11/site-packages/matplotlib/artist.py\", line 72, in draw_wrapper\n    return draw(artist, renderer)\n           ^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"\u003cpython_env\u003e/lib/python3.11/site-packages/matplotlib/axes/_base.py\", line 3137, in draw\n    mimage._draw_list_compositing_images(\n  File \"\u003cpython_env\u003e/lib/python3.11/site-packages/matplotlib/image.py\", line 132, in _draw_list_compositing_images\n    a.draw(renderer)\n  File \"\u003cpython_env\u003e/lib/python3.11/site-packages/matplotlib/artist.py\", line 72, in draw_wrapper\n    return draw(artist, renderer)\n           ^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"\u003cpython_env\u003e/lib/python3.11/site-packages/matplotlib/collections.py\", line 1005, in draw\n    super().draw(renderer)\n  File \"\u003cpython_env\u003e/lib/python3.11/site-packages/matplotlib/artist.py\", line 72, in draw_wrapper\n    return draw(artist, renderer)\n           ^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"\u003cpython_env\u003e/lib/python3.11/site-packages/matplotlib/collections.py\", line 426, in draw\n    renderer.draw_path_collection(\n  File \"\u003cpython_env\u003e/lib/python3.11/site-packages/matplotlib/backends/backend_pdf.py\", line 2074, in draw_path_collection\n    padding = np.max(linewidths)\n              ^^^^^^^^^^^^^^^^^^^^^^^\n  File \"\u003cpython_env\u003e/lib/python3.11/site-packages/numpy/core/fromnumeric.py\", line 2810, in max\n    return _wrapreduction(a, np.maximum, 'max', axis, None, out,\n           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"\u003cpython_env\u003e/lib/python3.11/site-packages/numpy/core/fromnumeric.py\", line 88, in _wrapreduction\n    return ufunc.reduce(obj, axis, dtype, out, **passkwargs)\n           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\nValueError: zero-size array to reduction operation maximum which has no identity\n```\n\n### Expected outcome\n\nThe error should be on the use of lw=\"\" in the scatter plot, but it should be coherent with the plt.show (which is not the case at the moment)\n\n### Additional information\n\nI don't know where the bug comes from, but I assume that \"ls\" is defined as a parameter of scatter, but is not uniformely treated in between the interactive window and the pdf backend.\n\n### Operating system\n\nMacOS 14.8.2, M1 pro processor.\n\n### Matplotlib Version\n\n3.9.2\n\n### Matplotlib Backend\n\nmacosx\n\n### Python version\n\n3.11.10\n\n### Jupyter version\n\n_No response_\n\n### Installation\n\nconda","author":{"url":"https://github.com/Nebulean","@type":"Person","name":"Nebulean"},"datePublished":"2026-04-29T12:17:14.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/31585/matplotlib/issues/31585"}