Merge pull request matplotlib#25334 from xtanion/contour_nan

Fix for all NANs in contour

Author: oscargus

lib/matplotlib/contour.py

@@ -1447,12 +1447,12 @@ def _contour_args(self, args, kwargs):
         else:
             raise _api.nargs_error(fn, takes="from 1 to 4", given=nargs)
         z = ma.masked_invalid(z, copy=False)
-        self.zmax = float(z.max())
-        self.zmin = float(z.min())
+        self.zmax = z.max().astype(float)
+        self.zmin = z.min().astype(float)
         if self.logscale and self.zmin <= 0:
             z = ma.masked_where(z <= 0, z)
             _api.warn_external('Log scale: values of z <= 0 have been masked')
-            self.zmin = float(z.min())
+            self.zmin = z.min().astype(float)
         self._process_contour_level_args(args, z.dtype)
         return (x, y, z)
 

lib/matplotlib/tests/test_contour.py

@@ -715,3 +715,10 @@ def test_bool_autolevel():
     assert plt.tricontour(x, y, z).levels.tolist() == [.5]
     assert plt.tricontourf(x, y, z.tolist()).levels.tolist() == [0, .5, 1]
     assert plt.tricontourf(x, y, z).levels.tolist() == [0, .5, 1]
+
+
+def test_all_nan():
+    x = np.array([[np.nan, np.nan], [np.nan, np.nan]])
+    assert_array_almost_equal(plt.contour(x).levels,
+                              [-1e-13, -7.5e-14, -5e-14, -2.4e-14, 0.0,
+                                2.4e-14, 5e-14, 7.5e-14, 1e-13])