BUG: np.ma.masked does not preserve identity through pickle

It's still possible to create duplicate MaskedConstants through `.copy()`

2 files changed, 15 insertions, 1 deletions

diff --git a/numpy/ma/core.py b/numpy/ma/core.py
index 2c62019cd..5cf859b75 100644
--- a/numpy/ma/core.py
+++ b/numpy/ma/core.py
@@ -6190,8 +6190,12 @@ class MaskedConstant(MaskedArray):
     _mask = mask = np.array(True)
     _baseclass = ndarray
 
+    __singleton = None
+
     def __new__(self):
-        return self._data.view(self)
+        if self.__singleton is None:
+            self.__singleton = self._data.view(self)
+        return self.__singleton
 
     def __array_finalize__(self, obj):
         return
diff --git a/numpy/ma/tests/test_core.py b/numpy/ma/tests/test_core.py
index 0a4840d41..345666317 100644
--- a/numpy/ma/tests/test_core.py
+++ b/numpy/ma/tests/test_core.py
@@ -4738,6 +4738,16 @@ class TestMaskedConstant(TestCase):
         assert_equal(repr(np.ma.masked), 'masked')
         assert_not_equal(repr(np.ma.masked.copy()), 'masked')
 
+    def test_pickle(self):
+        from io import BytesIO
+        import pickle
+
+        with BytesIO() as f:
+            pickle.dump(np.ma.masked, f)
+            f.seek(0)
+            res = pickle.load(f)
+        assert_(res is np.ma.masked)
+
 
 def test_masked_array():
     a = np.ma.array([0, 1, 2, 3], mask=[0, 0, 1, 0])