In SecondaryAxis.set_functions, reuse _set_scale's parent scale caching.

anntzer · anntzer · commit 650323abdbc2 · 2019-06-20T20:25:44.000+02:00
_set_scale checks whether the parent scale changed before modifying the
secondary scale.  set_functions should do the same.  See added test for
previously failing case.
diff --git a/lib/matplotlib/axes/_secondary_axes.py b/lib/matplotlib/axes/_secondary_axes.py
@@ -215,23 +215,7 @@ def set_functions(self, functions):
 
             If a transform is supplied, then the transform must have an
             inverse.
-
         """
-
-        if self._orientation == 'x':
-            set_scale = self.set_xscale
-            parent_scale = self._parent.get_xscale()
-        else:
-            set_scale = self.set_yscale
-            parent_scale = self._parent.get_yscale()
-        # we need to use a modified scale so the scale can receive the
-        # transform.  Only types supported are linear and log10 for now.
-        # Probably possible to add other transforms as a todo...
-        if parent_scale == 'log':
-            defscale = 'functionlog'
-        else:
-            defscale = 'function'
-
         if (isinstance(functions, tuple) and len(functions) == 2 and
             callable(functions[0]) and callable(functions[1])):
             # make an arbitrary convert from a two-tuple of functions
@@ -244,7 +228,7 @@ def set_functions(self, functions):
                              'must be a two-tuple of callable functions '
                              'with the first function being the transform '
                              'and the second being the inverse')
-        set_scale(defscale, functions=self._functions)
+        self._set_scale()
 
     def draw(self, renderer=None, inframe=False):
         """
diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
@@ -6135,6 +6135,16 @@ def invert(x):
                       mticker.NullLocator)
 
 
+def test_secondary_formatter():
+    fig, ax = plt.subplots()
+    ax.set_xscale("log")
+    secax = ax.secondary_xaxis("top")
+    secax.xaxis.set_major_formatter(mticker.ScalarFormatter())
+    fig.canvas.draw()
+    assert isinstance(
+        secax.xaxis.get_major_formatter(), mticker.ScalarFormatter)
+
+
 def color_boxes(fig, axs):
     """
     Helper for the tests below that test the extents of various axes elements
