LogFormatter bugfix, docs, support classic

Closes #7590. Classic style, with no minor tick labeling on a log axis, is supported via rcParams['_internal.classic'] LogFormatter changes are documented in api_changes and dflt_style_changes. An implicit boolean is made explicit in scale.py. A LogFormatter attribute that was sometimes, but not always, set by set_locs, but used only in __call__, is replaced by a local variable calculated in __call__. (set_locs doesn't have to be called prior to __call__, so this would have been a bug even if the attribute were always calculated by set_locs.)
matplotlib · dopplershift · Dec 9, 2016 · Dec 8, 2016 · Dec 8, 2016 · 1706340008a57e1e80c01091738b9a0b1cad4b92
commit 1706340008a57e1e80c01091738b9a0b1cad4b92
diff --git a/doc/api/api_changes.rst b/doc/api/api_changes.rst
@@ -141,6 +141,16 @@ the kwarg is None which internally sets it to the 'auto' string,
 triggering a new algorithm for adjusting the maximum according
 to the axis length relative to the ticklabel font size.
 
+`matplotlib.ticker.LogFormatter` gains minor_thresholds kwarg
+-------------------------------------------------------------
+
+Previously, minor ticks on log-scaled axes were not labeled by
+default.  An algorithm has been added to the
+`~matplotlib.ticker.LogFormatter` to control the labeling of
+ticks between integer powers of the base.  The algorithm uses
+two parameters supplied in a kwarg tuple named 'minor_thresholds'.
+See the docstring for further explanation.
+
 
 New defaults for 3D quiver function in mpl_toolkits.mplot3d.axes3d.py
 ---------------------------------------------------------------------

diff --git a/doc/users/dflt_style_changes.rst b/doc/users/dflt_style_changes.rst
@@ -1042,6 +1042,15 @@ Z-order
   ``rcParams['axes.axisbelow'] = False``.
 
 
+``LogFormatter`` labeling of minor ticks
+========================================
+
+Minor ticks on a log axis are now labeled when the axis view limits
+span a range less than or equal to the interval between two major
+ticks.  See `~matplotlib.ticker.LogFormatter` for details. The
+minor tick labeling is turned off when using ``mpl.style.use('classic')``,
+but cannot be controlled independently via ``rcParams``.
+
 
 ``ScalarFormatter`` tick label formatting with offsets
 ======================================================

diff --git a/lib/matplotlib/scale.py b/lib/matplotlib/scale.py
@@ -251,7 +251,7 @@ def set_default_locators_and_formatters(self, axis):
         axis.set_minor_locator(LogLocator(self.base, self.subs))
         axis.set_minor_formatter(
             LogFormatterSciNotation(self.base,
-                                    labelOnlyBase=self.subs))
+                                    labelOnlyBase=bool(self.subs)))
 
     def get_transform(self):
         """

diff --git a/lib/matplotlib/tests/test_ticker.py b/lib/matplotlib/tests/test_ticker.py
@@ -231,7 +231,7 @@ def _sub_labels(axis, subs=()):
     assert_equal(label_test, label_expected)
 
 
-@cleanup
+@cleanup(style='default')
 def test_LogFormatter_sublabel():
     # test label locator
     fig, ax = plt.subplots()

diff --git a/lib/matplotlib/ticker.py b/lib/matplotlib/ticker.py
@@ -837,7 +837,12 @@ class LogFormatter(Formatter):
     major and minor ticks; the tick locations might be set manually,
     or by a locator that puts ticks at integer powers of base and
     at intermediate locations.  For this situation, disable the
-    minor_thresholds logic by using ``minor_thresholds=(np.inf, np.inf)``.
+    minor_thresholds logic by using ``minor_thresholds=(np.inf, np.inf)``,
+    so that all ticks will be labeled.
+
+    To disable labeling of minor ticks when 'labelOnlyBase' is False,
+    use ``minor_thresholds=(0, 0)``.  This is the default for the
+    "classic" style.
 
     Examples
     --------
@@ -848,14 +853,18 @@ class LogFormatter(Formatter):
     To label all minor ticks when the view limits span up to 1.5
     decades, use ``minor_thresholds=(1.5, 1.5)``.
 
-
     """
     def __init__(self, base=10.0, labelOnlyBase=False,
-                 minor_thresholds=(1, 0.4),
+                 minor_thresholds=None,
                  linthresh=None):
 
         self._base = float(base)
         self.labelOnlyBase = labelOnlyBase
+        if minor_thresholds is None:
+            if rcParams['_internal.classic_mode']:
+                minor_thresholds = (0, 0)
+            else:
+                minor_thresholds = (1, 0.4)
         self.minor_thresholds = minor_thresholds
         self._sublabels = None
         self._linthresh = linthresh
@@ -896,7 +905,6 @@ def set_locs(self, locs=None):
         b = self._base
 
         vmin, vmax = self.axis.get_view_interval()
-        self.d = abs(vmax - vmin)
 
         # Handle symlog case:
         linthresh = self._linthresh
@@ -937,6 +945,9 @@ def __call__(self, x, pos=None):
         """
         Return the format for tick val `x`.
         """
+        vmin, vmax = self.axis.get_view_interval()
+        vmin, vmax = mtransforms.nonsingular(vmin, vmax, expander=0.05)
+        d = abs(vmax - vmin)
         b = self._base
         if x == 0.0:
             return '0'
@@ -957,7 +968,7 @@ def __call__(self, x, pos=None):
         elif x < 1:
             s = '%1.0e' % x
         else:
-            s = self.pprint_val(x, self.d)
+            s = self.pprint_val(x, d)
         if sign == -1:
             s = '-%s' % s