Fix format_cursor_data with nans.

anntzer · anntzer · commit fe4b36b32f9c · 2021-09-21T17:10:06.000+02:00
Without this fix, hovering the mouse over a nan pixel in an imshow()
would result in `Warning: converting a masked element to nan.` and then
`ValueError: cannot convert float NaN to integer`.  Fix that.

The format_cursor_data test doesn't explicitly check the return value
of get_cursor_data anymore because np.ma.masked is returned for nan
inputs (this is expected from the general approach for handling invalid
data); checking that format_cursor_data gives the right string is
sufficient.
diff --git a/lib/matplotlib/artist.py b/lib/matplotlib/artist.py
@@ -1273,6 +1273,8 @@ def format_cursor_data(self, data):
             # from Artist first and from ScalarMappable second, so
             # Artist.format_cursor_data would always have precedence over
             # ScalarMappable.format_cursor_data.
+            if np.ma.getmask(data):
+                return "[]"
             n = self.cmap.N
             # Midpoints of neighboring color intervals.
             neighbors = self.norm.inverse(
diff --git a/lib/matplotlib/tests/test_image.py b/lib/matplotlib/tests/test_image.py
@@ -340,6 +340,7 @@ def test_cursor_data():
     "data, text", [
         ([[10001, 10000]], "[10001.000]"),
         ([[.123, .987]], "[0.123]"),
+        ([[np.nan, 1, 2]], "[]"),
     ])
 def test_format_cursor_data(data, text):
     from matplotlib.backend_bases import MouseEvent
@@ -349,7 +350,6 @@ def test_format_cursor_data(data, text):
 
     xdisp, ydisp = ax.transData.transform([0, 0])
     event = MouseEvent('motion_notify_event', fig.canvas, xdisp, ydisp)
-    assert im.get_cursor_data(event) == data[0][0]
     assert im.format_cursor_data(im.get_cursor_data(event)) == text
 
 
