Use format_data_short to format image cursor data.

anntzer · anntzer · commit 351a080b339a · 2019-03-17T16:10:17.000+01:00
Despite its name, format_data_short is actually used to format the x/y
cursor data; it makes sense to also use it for image data.  By doing so,
e.g. for `imshow([[.123, .987]])`, one gets the more accurate `.123`
string when the mouse is over the first pixel instead of `.1` that
`__call__` returns (which would have been intended as a tick label).
diff --git a/doc/users/next_whats_new/2018-10-10-AL.rst b/doc/users/next_whats_new/2018-10-10-AL.rst
@@ -4,6 +4,5 @@ Improved formatting of image values under cursor when a colorbar is present
 When a colorbar is present, its formatter is now used to format the image
 values under the mouse cursor in the status bar.  For example, for an image
 displaying the values 10,000 and 10,001, the statusbar will now (using default
-settings) display the values as ``0.0+1e4`` and ``1.0+1e4`` (or ``10000.0``
-and ``10001.0`` if the offset-text is disabled on the colorbar), whereas both
-values were previously displayed as ``1e+04``.
+settings) display the values as ``10000`` and ``10001``), whereas both values
+were previously displayed as ``1e+04``.
diff --git a/lib/matplotlib/image.py b/lib/matplotlib/image.py
@@ -934,10 +934,11 @@ def get_cursor_data(self, event):
 
     def format_cursor_data(self, data):
         if self.colorbar:
-            return ("["
-                    + cbook.strip_math(self.colorbar.formatter(data))
-                    + cbook.strip_math(self.colorbar.formatter.get_offset())
-                    + "]")
+            return (
+                "["
+                + cbook.strip_math(
+                    self.colorbar.formatter.format_data_short(data)).strip()
+                + "]")
         else:
             return super().format_cursor_data(data)
 
diff --git a/lib/matplotlib/tests/test_image.py b/lib/matplotlib/tests/test_image.py
@@ -291,22 +291,29 @@ def test_cursor_data():
     assert im.get_cursor_data(event) is None
 
 
-def test_format_cursor_data():
+@pytest.mark.parametrize(
+    "data, text_without_colorbar, text_with_colorbar", [
+        ([[10001, 10000]], "[1e+04]", "[10001]"),
+        ([[.123, .987]], "[0.123]", "[0.123]"),
+])
+def test_format_cursor_data(data, text_without_colorbar, text_with_colorbar):
     from matplotlib.backend_bases import MouseEvent
 
     fig, ax = plt.subplots()
-    im = ax.imshow([[10000, 10001]])
+    im = ax.imshow(data)
 
     xdisp, ydisp = ax.transData.transform_point([0, 0])
     event = MouseEvent('motion_notify_event', fig.canvas, xdisp, ydisp)
-    assert im.get_cursor_data(event) == 10000
-    assert im.format_cursor_data(im.get_cursor_data(event)) == "[1e+04]"
+    assert im.get_cursor_data(event) == data[0][0]
+    assert im.format_cursor_data(im.get_cursor_data(event)) \
+        == text_without_colorbar
 
     fig.colorbar(im)
     fig.canvas.draw()  # This is necessary to set up the colorbar formatter.
 
-    assert im.get_cursor_data(event) == 10000
-    assert im.format_cursor_data(im.get_cursor_data(event)) == "[0.0+1e4]"
+    assert im.get_cursor_data(event) == data[0][0]
+    assert im.format_cursor_data(im.get_cursor_data(event)) \
+        == text_with_colorbar
 
 
 @image_comparison(baseline_images=['image_clip'], style='mpl20')
