add axes.formatter.offset_threshold rcParam: classic is 2, v2.0 is 4

Author: efiring

lib/matplotlib/mpl-data/stylelib/classic.mplstyle

@@ -204,6 +204,10 @@ axes.formatter.useoffset      : True    # If True, the tick label formatter
                                         # to an offset when the data range is very
                                         # small compared to the minimum absolute
                                         # value of the data.
+axes.formatter.offset_threshold : 2      # When useoffset is True, the offset
+                                         # will be used when it can remove
+                                         # at least this number of significant
+                                         # digits from tick labels.
 
 axes.unicode_minus  : True    # use unicode for the minus symbol
                               # rather than hyphen.  See

lib/matplotlib/rcsetup.py

@@ -1085,6 +1085,7 @@ def validate_animation_writer_path(p):
                                # Use the current locale to format ticks
     'axes.formatter.use_mathtext': [False, validate_bool],
     'axes.formatter.useoffset': [True, validate_bool],
+    'axes.formatter.offset_threshold': [4, validate_int],
     'axes.unicode_minus': [True, validate_bool],
     'axes.color_cycle': [
         ['#1f77b4', '#ff7f0e', '#2ca02c', '#d62728',

lib/matplotlib/tests/test_ticker.py

@@ -169,7 +169,7 @@ def test_SymmetricalLogLocator_set_params():
     nose.tools.assert_equal(sym.numticks, 8)
 
 
-@cleanup
+@cleanup(style='classic')
 def test_ScalarFormatter_offset_value():
     fig, ax = plt.subplots()
     formatter = ax.get_xaxis().get_major_formatter()

lib/matplotlib/ticker.py

@@ -505,6 +505,7 @@ def __init__(self, useOffset=None, useMathText=None, useLocale=None):
 
         if useOffset is None:
             useOffset = rcParams['axes.formatter.useoffset']
+        self._offset_threshold = rcParams['axes.formatter.offset_threshold']
         self.set_useOffset(useOffset)
         self._usetex = rcParams['text.usetex']
         if useMathText is None:
@@ -689,9 +690,10 @@ def _compute_offset(self):
             # are no more than 1 apart at that precision?
             oom = 1 + next(oom for oom in itertools.count(oom_max, -1)
                            if abs_max // 10 ** oom - abs_min // 10 ** oom > 1)
-        # Only use offset if it saves at least 4 significant digits.
+        # Only use offset if it saves at least _offset_threshold digits.
+        n = self._offset_threshold - 1
         self.offset = (sign * (abs_max // 10 ** oom) * 10 ** oom
-                       if abs_max // 10 ** oom >= 10**3  # 10**(4-1)
+                       if abs_max // 10 ** oom >= 10**n
                        else 0)
 
     def _set_orderOfMagnitude(self, range):

matplotlibrc.template

@@ -317,10 +317,13 @@ backend      : $TEMPLATE_BACKEND
                                      # notation.
 #axes.formatter.useoffset      : True    # If True, the tick label formatter
                                          # will default to labeling ticks relative
-                                         # to an offset when the data range is very
+                                         # to an offset when the data range is
                                          # small compared to the minimum absolute
                                          # value of the data.
-
+#axes.formatter.offset_threshold : 4     # When useoffset is True, the offset
+                                         # will be used when it can remove
+                                         # at least this number of significant
+                                         # digits from tick labels.
 
 #axes.unicode_minus  : True    # use unicode for the minus symbol
                                # rather than hyphen.  See