From 8f924d40645f13a73b7896884d86f7a1472a71f0 Mon Sep 17 00:00:00 2001
From: cvanelteren <caspervanelteren@gmail.com>
Date: Tue, 30 Dec 2025 07:35:57 +1000
Subject: [PATCH] Preserve log formatter when setting log scales

---
 ultraplot/axes/cartesian.py  | 68 ++++++++++++++++++++++++++++++++----
 ultraplot/tests/test_plot.py | 27 ++++++++++++++
 2 files changed, 89 insertions(+), 6 deletions(-)

diff --git a/ultraplot/axes/cartesian.py b/ultraplot/axes/cartesian.py
index 46685b5df..b19047542 100644
--- a/ultraplot/axes/cartesian.py
+++ b/ultraplot/axes/cartesian.py
@@ -5,22 +5,27 @@
 import copy
 import inspect
 
+import matplotlib.axis as maxis
 import matplotlib.dates as mdates
 import matplotlib.ticker as mticker
 import numpy as np
-
 from packaging import version
 
 from .. import constructor
 from .. import scale as pscale
 from .. import ticker as pticker
 from ..config import rc
-from ..internals import ic  # noqa: F401
-from ..internals import _not_none, _pop_rc, _version_mpl, docstring, labels, warnings
-from . import plot, shared
-import matplotlib.axis as maxis
-
+from ..internals import (
+    _not_none,
+    _pop_rc,
+    _version_mpl,
+    docstring,
+    ic,  # noqa: F401
+    labels,
+    warnings,
+)
 from ..utils import units
+from . import plot, shared
 
 __all__ = ["CartesianAxes"]
 
@@ -779,6 +784,26 @@ def _sharey_setup(self, sharey, *, labels=True, limits=True):
         if level > 1 and limits:
             self._sharey_limits(sharey)
 
+    def _apply_log_formatter_on_scale(self, s):
+        """
+        Enforce log formatter when log scale is set and rc is enabled.
+        """
+        if not rc.find("formatter.log", context=True):
+            return
+        if getattr(self, f"get_{s}scale")() != "log":
+            return
+        self._update_formatter(s, "log")
+
+    def set_xscale(self, value, **kwargs):
+        result = super().set_xscale(value, **kwargs)
+        self._apply_log_formatter_on_scale("x")
+        return result
+
+    def set_yscale(self, value, **kwargs):
+        result = super().set_yscale(value, **kwargs)
+        self._apply_log_formatter_on_scale("y")
+        return result
+
     def _update_formatter(
         self,
         s,
@@ -1389,6 +1414,7 @@ def format(
                 # WARNING: Changing axis scale also changes default locators
                 # and formatters, and restricts possible range of axis limits,
                 # so critical to do it first.
+                scale_requested = scale is not None
                 if scale is not None:
                     scale = constructor.Scale(scale, **scale_kw)
                     getattr(self, f"set_{s}scale")(scale)
@@ -1480,10 +1506,40 @@ def format(
                     tickrange=tickrange,
                     wraprange=wraprange,
                 )
+                if (
+                    scale_requested
+                    and formatter is None
+                    and not formatter_kw
+                    and tickrange is None
+                    and wraprange is None
+                    and rc.find("formatter.log", context=True)
+                    and getattr(self, f"get_{s}scale")() == "log"
+                ):
+                    self._update_formatter(s, "log")
 
                 # Ensure ticks are within axis bounds
                 self._fix_ticks(s, fixticks=fixticks)
 
+        if rc.find("formatter.log", context=True):
+            if (
+                xscale is not None
+                and xformatter is None
+                and not xformatter_kw
+                and xtickrange is None
+                and xwraprange is None
+                and self.get_xscale() == "log"
+            ):
+                self._update_formatter("x", "log")
+            if (
+                yscale is not None
+                and yformatter is None
+                and not yformatter_kw
+                and ytickrange is None
+                and ywraprange is None
+                and self.get_yscale() == "log"
+            ):
+                self._update_formatter("y", "log")
+
         # Parent format method
         if aspect is not None:
             self.set_aspect(aspect)
diff --git a/ultraplot/tests/test_plot.py b/ultraplot/tests/test_plot.py
index fb54d191a..1bcb69684 100644
--- a/ultraplot/tests/test_plot.py
+++ b/ultraplot/tests/test_plot.py
@@ -361,6 +361,33 @@ def reset(ax):
     uplt.close(fig)
 
 
+def test_format_log_scale_preserves_log_formatter():
+    """
+    Test that setting a log scale preserves the log formatter when enabled.
+    """
+    x = np.linspace(1, 1e6, 10)
+    log_formatter = uplt.constructor.Formatter("log")
+    log_formatter_type = type(log_formatter)
+
+    with uplt.rc.context({"formatter.log": True}):
+        fig, ax = uplt.subplots()
+        ax.plot(x, x)
+        ax.format(yscale="log")
+        assert isinstance(ax.yaxis.get_major_formatter(), log_formatter_type)
+        ax.set_yscale("log")
+        assert isinstance(ax.yaxis.get_major_formatter(), log_formatter_type)
+
+    with uplt.rc.context({"formatter.log": False}):
+        fig, ax = uplt.subplots()
+        ax.plot(x, x)
+        ax.format(yscale="log")
+        assert not isinstance(ax.yaxis.get_major_formatter(), log_formatter_type)
+        ax.set_yscale("log")
+        assert not isinstance(ax.yaxis.get_major_formatter(), log_formatter_type)
+
+    uplt.close(fig)
+
+
 def test_shading_pcolor(rng):
     """
     Pcolormesh by default adjusts the plot by