BUG: __copy__ and __deepcopy__ should preserve MaskedConstant (#11038)

Fixes #11021

2 files changed, 16 insertions, 0 deletions

diff --git a/numpy/ma/core.py b/numpy/ma/core.py
index fb28fa8e5..c0dda6f31 100644
--- a/numpy/ma/core.py
+++ b/numpy/ma/core.py
@@ -6317,6 +6317,12 @@ class MaskedConstant(MaskedArray):
         # precedent for this with `np.bool_` scalars.
         return self
 
+    def __copy__(self):
+        return self
+		
+    def __deepcopy__(self, memo):
+        return self
+
     def __setattr__(self, attr, value):
         if not self.__has_singleton():
             # allow the singleton to be initialized
diff --git a/numpy/ma/tests/test_core.py b/numpy/ma/tests/test_core.py
index 63703f6cd..4c7440aab 100644
--- a/numpy/ma/tests/test_core.py
+++ b/numpy/ma/tests/test_core.py
@@ -4826,6 +4826,16 @@ class TestMaskedConstant(object):
             np.ma.masked.copy() is np.ma.masked,
             np.True_.copy() is np.True_)
 
+    def test__copy(self):
+        import copy
+        assert_(
+            copy.copy(np.ma.masked) is np.ma.masked)
+
+    def test_deepcopy(self):
+        import copy
+        assert_(
+            copy.deepcopy(np.ma.masked) is np.ma.masked)
+
     def test_immutable(self):
         orig = np.ma.masked
         assert_raises(np.ma.core.MaskError, operator.setitem, orig, (), 1)