Fix mpl bug where altx/y resets log minor locator

Author: lukelbd

proplot/axes/cartesian.py

@@ -1195,13 +1195,23 @@ def altx(self, **kwargs):
         """
         %(axes.altx)s
         """
-        # Cannot wrap twiny() because we want to use CartesianAxes, not
-        # matplotlib Axes. Instead use hidden method _make_twin_axes.
-        # See https://github.com/matplotlib/matplotlib/blob/master/lib/matplotlib/axes/_subplots.py  # noqa
+        # NOTE: Cannot *wrap* twiny() because we want to use CartesianAxes, not
+        # matplotlib Axes. Instead use hidden method SubplotBase._make_twin_axes.
+        # WARNING: This repairs a matplotlib bug where twins fail to inherit the minor
+        # locator due to application of `AutoMinorLocator` when `ytick.minor.visible`
+        # is ``True`` in `Axes.cla` and due to the fact that passing ``sharey=self``
+        # to the alternate axes means that they share the same major and minor Tickers.
+        # >>> import matplotlib.pyplot as plt
+        # ... fig, ax = plt.subplots()
+        # ... ax.set_yscale('log')
+        # ... ax.twiny()
         if self._altx_child or self._altx_parent:
             raise RuntimeError('No more than *two* twin axes are allowed.')
         with self.figure._context_authorize_add_subplot():
+            ylocator = self.yaxis.get_minor_locator()
             ax = self._make_twin_axes(sharey=self, projection='cartesian')
+            ax.yaxis.set_minor_locator(ylocator)
+            ax.yaxis.isDefault_minloc = True
         ax.set_autoscaley_on(self.get_autoscaley_on())
         ax.grid(False)
         self._altx_child = ax
@@ -1218,11 +1228,14 @@ def alty(self, **kwargs):
         """
         %(axes.alty)s
         """
-        # Docstring is programatically assigned below
+        # See altx() comments
         if self._alty_child or self._alty_parent:
             raise RuntimeError('No more than *two* twin axes are allowed.')
         with self.figure._context_authorize_add_subplot():
+            xlocator = self.xaxis.get_minor_locator()
             ax = self._make_twin_axes(sharex=self, projection='cartesian')
+            ax.xaxis.set_minor_locator(xlocator)
+            ax.xaxis.isDefault_minloc = True
         ax.set_autoscalex_on(self.get_autoscalex_on())
         ax.grid(False)
         self._alty_child = ax

proplot/axes/plot.py

@@ -522,14 +522,15 @@ def standardize_1d(self, func, *args, autoformat=None, **kwargs):
             if label and not getattr(self, f'get_{iname}label')():
                 # For histograms, this label is used for *x* coordinates
                 kw[iname + 'label'] = label
-            # Xlabel
             if name not in ('hist',):
+                # Xlabel
                 x, label = _axis_labels_title(x)
                 if label and not getattr(self, f'get_{xname}label')():
                     kw[xname + 'label'] = label
-            # Reversed axis
-            if name not in ('scatter',) and len(x) > 1 and xi is None and x[1] < x[0]:
-                kw[xname + 'reverse'] = True
+                # Reversed axis
+                if name not in ('scatter',):
+                    if len(x) > 1 and xi is None and x[1] < x[0]:
+                        kw[xname + 'reverse'] = True
 
         # Appply
         if kw: