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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"On making the rc-validators function know the rcParam affected instance","articleBody":"The RcParams class is probably treated as a singleton (with rcParams as the sole instance) by nearly everyone.  I now have two cases where I either need to rely on this assumption, or at least need to make a rc-validator function know the actual RcParam instance that is being modified (if RcParam is a singleton, then we of course know what instance is being modified -- there's only one instance!).\r\n\r\nCase 1) is #9795 (backend-switching), where I propose that assigning to `rcParams[\"backend\"]` also sets the backend (currently, this has no effect after pyplot is imported, but I believe having `rcParams[\"backend\"]` and the actual backend go out of sync is particularly bad in a world where backend-switching becomes better supported).  But of course, the actual backend in use is global state, so the backend switch (which is implemented in the rc-validator function) should only occur if the currently modified instance `is mpl.rcParams`.\r\n\r\nCase 2) is #11231, where I propose replacing multiple rcParams (`figure.subplot.{left,right,...}`) by a single one (`figure.subplot`).  During the deprecation period, changes to `figure.subplot.{left,right,...}` need to be propagated to `figure.subplot` in the same instance, and vice-versa.\r\n\r\nMaking rcParams a singleton (for most purposes) is not particularly difficult (override `__new__`, yada yada) but perhaps inelegant?  Making the validators know the currently modified instance is not too hard either, as all validators currently take a single argument (and no optional argument), so we can just say e.g. \"if a validator takes two arguments (this can easily be checked at the very beginning), pass the RcParams instance as first/second argument\".\r\n\r\nThoughts?\r\n\r\n(Milestoning as 3.0 as it would be nice to resolve this before #9795, but that's not strictly necessary either as we can just make/document the assumption too.)\r\n\r\nEdit: dates.converter and dates.interval_multiples are also entries that now assume that there's just a single rcParams instance, as assigning to them (regardless of whether it's on the main instance or not) always updates the global state regarding date formatters.","author":{"url":"https://github.com/anntzer","@type":"Person","name":"anntzer"},"datePublished":"2018-06-26T00:17:31.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":4},"url":"https://github.com/11509/matplotlib/issues/11509"}