FIX: formatting in LogFormatterExponent

The scale passed to the `pprint_val` method needs to also be scaled by the log so that the range used to format the tick labels matches the actual range of the tick labels (not the underlying values). reported via http://stackoverflow.com/questions/33975758/matplotlib-logformatterexponent-e-in-the-exponent-labels-of-cbar
matplotlib · mdboom · Dec 14, 2015 · Dec 1, 2015 · Dec 1, 2015 · Dec 1, 2015
commit 7e3ef7dc2095852fbd3a668c4a0d3285a63e6ee3
diff --git a/lib/matplotlib/tests/test_ticker.py b/lib/matplotlib/tests/test_ticker.py
@@ -159,20 +159,28 @@ def test_SymmetricalLogLocator_set_params():
    nose.tools.assert_equal(sym.numticks, 8)


+def _logfe_helper(formatter, base, locs, i, expected_result):
+    vals = base**locs
+    labels = [formatter(x, pos) for (x, pos) in zip(vals, i)]
+    nose.tools.assert_equal(labels, expected_result)
+
+
 def test_LogFormatterExponent():
    class FakeAxis(object):
        """Allow Formatter to be called without having a "full" plot set up."""
+        def __init__(self, vmin=1, vmax=10):
+            self.vmin = vmin
+            self.vmax = vmax
+
        def get_view_interval(self):
-            return 1, 10
+            return self.vmin, self.vmax

    i = np.arange(-3, 4, dtype=float)
    expected_result = ['-3', '-2', '-1', '0', '1', '2', '3']
-    for base in [2, 5, 10, np.pi, np.e]:
+    for base in [2, 5.0, 10.0, np.pi, np.e]:
        formatter = mticker.LogFormatterExponent(base=base)
-        formatter.axis = FakeAxis()
-        vals = base**i
-        labels = [formatter(x, pos) for (x, pos) in zip(vals, i)]
-        nose.tools.assert_equal(labels, expected_result)
+        formatter.axis = FakeAxis(1, base**4)
+        yield _logfe_helper, formatter, base, i, i, expected_result

    # Should be a blank string for non-integer powers if labelOnlyBase=True
    formatter = mticker.LogFormatterExponent(base=10, labelOnlyBase=True)
@@ -185,10 +193,15 @@ def get_view_interval(self):
    expected_result = ['0.1', '1e-05', '3.14', '0.2', '-0.2', '-1e-05']
    for base in [2, 5, 10, np.pi, np.e]:
        formatter = mticker.LogFormatterExponent(base, labelOnlyBase=False)
-        formatter.axis = FakeAxis()
-        vals = base**locs
-        labels = [formatter(x, pos) for (x, pos) in zip(vals, i)]
-        nose.tools.assert_equal(labels, expected_result)
+        formatter.axis = FakeAxis(1, base**10)
+        yield _logfe_helper, formatter, base, locs, i, expected_result
+
+    expected_result = ['3', '5', '12', '42']
+    locs = np.array([3, 5, 12, 42], dtype='float')
+    for base in [2, 5.0, 10.0, np.pi, np.e]:
+        formatter = mticker.LogFormatterExponent(base, labelOnlyBase=False)
+        formatter.axis = FakeAxis(1, base**50)
+        yield _logfe_helper, formatter, base, locs, i, expected_result


 def test_use_offset():

diff --git a/lib/matplotlib/ticker.py b/lib/matplotlib/ticker.py
@@ -768,7 +768,8 @@ def __call__(self, x, pos=None):
        elif abs(fx) < 1:
            s = '%1.0g' % fx
        else:
-            s = self.pprint_val(fx, d)
+            fd = math.log(abs(d)) / math.log(b)
+            s = self.pprint_val(fx, fd)
        if sign == -1:
            s = '-%s' % s