MNT: Move "backend" from a regular rcParams dict entry to a class attribute#31792
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timhoffm wants to merge 1 commit into
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MNT: Move "backend" from a regular rcParams dict entry to a class attribute#31792timhoffm wants to merge 1 commit into
timhoffm wants to merge 1 commit into
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…ribute Working towards matplotlib#31791. > rcParams should be only configuration, not state; i.e. wrt. backend, it > can hold the desired backend and backend priorities, but it should not > hold the currently active backend or trigger backend selection as a > side-effect. The latter causes a lot of complexity in rcParams. This PR is the first step in the migration strategy outlined there: > Make the backend a RcParams class attribute and do not hold > "backend" as a regular dict entry. There can only be one backend, > so putting that value in a class attribute `RcParams._backend` makes > sense. This already reduces the complexity as we don't need special > handling to sync/copy the value when rcParams are bulk-replaced > (loading from file or rc_context). Instead add special logic to keep > behavioral backward compatibility with the dict API > (`rcParams["backend"]` / `rcParams._get("backend")` / > `"rcParams._set("backend", val)`). Note on API compatibility: This PR limits itself to the known typical dict-API usages in the context of backend handling. I've refrained from trying to fully replicate dict behavior of a "virtual" "backend" parameter, i.e. `len(rcParams)` / `rcParams.keys()` / `rcParams.values()` / `rcParams.items()` do not contain "backend" anymore. I would be willing to accept this level of API breakage. If deemed critical, we could add compatibility shims for that too.
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timhoffm
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May 31, 2026
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| def _ensure_has_backend(self): | ||
| """ | ||
| Ensure that a "backend" entry exists. | ||
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| Normally, the default matplotlibrc file contains *no* entry for "backend" (the | ||
| corresponding line starts with ##, not #; we fill in _auto_backend_sentinel | ||
| in that case. However, packagers can set a different default backend | ||
| (resulting in a normal `#backend: foo` line) in which case we should *not* | ||
| fill in _auto_backend_sentinel. | ||
| """ | ||
| dict.setdefault(self, "backend", rcsetup._auto_backend_sentinel) |
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Note: _ensure_has_backend() is not needed anymore, because the backend is stored in the class attribute RcParams._backend and thus always available.
timhoffm
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May 31, 2026
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| orig = dict(rcParams.copy()) | ||
| del orig['backend'] |
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Note: The dict conversion was only needed to be able to drop the backend entry. Since that doesn't exist anymore, we don't need the dict conversion.
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PR summary
Working towards #31791.
This PR is the first step in the migration strategy outlined there:
Note on API compatibility: This PR limits itself to the known typical dict-API usages in the context of backend handling. I've refrained from trying to fully replicate dict behavior of a "virtual" "backend" parameter, i.e.
len(rcParams)/rcParams.keys()/rcParams.values()/rcParams.items()do not contain "backend" anymore. I would be willing to accept this level of API breakage. If deemed critical, we could add compatibility shims for that too, but it's a bit more complicated as the style variants of RcParams must not claim to have "backend" as a key.AI Disclosure
AI was used to analyze the code base and draft an implementation proposal. I've thoroughly reviewed and modified the result to the present form.
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