MAINT: Warn users when calling np.ma.MaskedArray.(arg-)partition function.

Using the np.median function on MaskedArrays uses the not-overriden
partition method of a plain np.ndarray without error or warning. (#7330)
This PR overrides the partition method on MaskedArrays but simply to
throw a Warning. This will make users aware that something ignores the
mask without breaking backwards-compatibility. This also applies to
the argpartition method (even if it's not called by np.median).

1 files changed, 12 insertions, 0 deletions

diff --git a/numpy/ma/core.py b/numpy/ma/core.py
index af8a523ab..ea4a1d85f 100644
--- a/numpy/ma/core.py
+++ b/numpy/ma/core.py
@@ -5635,6 +5635,18 @@ class MaskedArray(ndarray):
         np.subtract(out, min_value, out=out, casting='unsafe')
         return out
 
+    def partition(self, *args, **kwargs):
+        warnings.warn("Warning: 'partition' will ignore the 'mask' "
+                      "of the {}.".format(self.__class__.__name__),
+                      stacklevel=2)
+        return super(MaskedArray, self).partition(*args, **kwargs)
+
+    def argpartition(self, *args, **kwargs):
+        warnings.warn("Warning: 'argpartition' will ignore the 'mask' "
+                      "of the {}.".format(self.__class__.__name__),
+                      stacklevel=2)
+        return super(MaskedArray, self).argpartition(*args, **kwargs)
+
     def take(self, indices, axis=None, out=None, mode='raise'):
         """
         """