DEP: Add warnings to `__getitem__` and `__setitem__` to point out the behavior of `MaskedArray`'s masks is changing.

1 files changed, 17 insertions, 0 deletions

diff --git a/numpy/ma/core.py b/numpy/ma/core.py
index 6b1f09f19..690655b36 100644
--- a/numpy/ma/core.py
+++ b/numpy/ma/core.py
@@ -3105,6 +3105,14 @@ class MaskedArray(ndarray):
         Return the item described by i, as a masked array.
 
         """
+        # 2016.01.15 -- v1.11.0
+        warnings.warn(
+            "Currently, slicing will try to return a view of the data," +
+            " but will return a copy of the mask. In the future, it will try" +
+            " to return both as views.",
+            FutureWarning
+        )
+
         dout = self.data[indx]
         # We could directly use ndarray.__getitem__ on self.
         # But then we would have to modify __array_finalize__ to prevent the
@@ -3175,6 +3183,15 @@ class MaskedArray(ndarray):
         locations.
 
         """
+        # 2016.01.15 -- v1.11.0
+        warnings.warn(
+           "Currently, slicing will try to return a view of the data," +
+           " but will return a copy of the mask. In the future, it will try" +
+           " to return both as views. This means that using `__setitem__`" +
+           " will propagate values back through all masks that are present.",
+           FutureWarning
+        )
+
         if self is masked:
             raise MaskError('Cannot alter the masked element.')
         _data = self._data