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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"[ENH]: Make \"No artists with labels found to put in legend\" a warning","articleBody":"### Problem\r\n\r\nWhen I receive this issue, it's hard to debug and find the specific call to `ax.legend()`  if I can't raise Warnings to Exceptions.  I sometimes nest plotting functions in order to draw the same plot different ways or arrange plots in a composite figure, depending upon the presentation.\r\n\r\nMWE and Full message:\r\n\r\n```python\r\nfrom matplotlib import pyplot as plt\r\nimport warnings\r\n\r\nwarnings.simplefilter(\"error\", category=Warning)\r\nplt.plot([1,2,3])\r\nplt.legend()\r\n```\r\n(no error, plot appears)\r\n\u003e No artists with labels found to put in legend.  Note that artists whose label start with an underscore are ignored when legend() is called with no argument.\r\n\r\n### Proposed solution\r\n\r\nMake this a true `UserWarning`.  Currently, it's a `logging.LogRecord` of level=`logging.Warning`.  \r\n```python\r\nlog = logging.getLogger(__name__)\r\n...\r\nlog.warning(\u003cthis message\u003e)\r\n```\r\n**Additional pro:** In the future, it would be easier to find and work on this warning if it is, in fact, a true `Warning`.\r\n\r\n**Con:** It won't be handled by the logging infrastructure.  But legend.py uses the default module logger, and the only `LogRecord` that it emits is this one.  The only situation I could think of where this might matter is if a user has some override of global logging setup (by calling `logging.setLoggerClass()`) but does not apply a similar philosophy to capturing warnings in STDERR.\r\n","author":{"url":"https://github.com/Jacob-Stevens-Haas","@type":"Person","name":"Jacob-Stevens-Haas"},"datePublished":"2023-10-19T13:51:10.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":8},"url":"https://github.com/27145/matplotlib/issues/27145"}