BUG: ma.put expands nomask

Previously when put was used on a MaskedArray with nomask the mask would be
incorrectly set to the mask of the values argument.

closes #6425

2 files changed, 25 insertions, 9 deletions

diff --git a/numpy/ma/core.py b/numpy/ma/core.py
index 9e8dad08c..698416579 100644
--- a/numpy/ma/core.py
+++ b/numpy/ma/core.py
@@ -4399,7 +4399,6 @@ class MaskedArray(ndarray):
          [7 -- 30]]
 
         """
-        m = self._mask
         # Hard mask: Get rid of the values/indices that fall on masked data
         if self._hardmask and self._mask is not nomask:
             mask = self._mask[indices]
@@ -4411,16 +4410,19 @@ class MaskedArray(ndarray):
 
         self._data.put(indices, values, mode=mode)
 
-        if m is nomask:
-            m = getmask(values)
+        # short circut if neither self nor values are masked
+        if self._mask is nomask and getmask(values) is nomask:
+            return
+
+        m = getmaskarray(self).copy()
+
+        if getmask(values) is nomask:
+            m.put(indices, False, mode=mode)
         else:
-            m = m.copy()
-            if getmask(values) is nomask:
-                m.put(indices, False, mode=mode)
-            else:
-                m.put(indices, values._mask, mode=mode)
-            m = make_mask(m, copy=False, shrink=True)
+            m.put(indices, values._mask, mode=mode)
+        m = make_mask(m, copy=False, shrink=True)
         self._mask = m
+        return
 
     def ids(self):
         """
diff --git a/numpy/ma/tests/test_core.py b/numpy/ma/tests/test_core.py
index 550f03131..f832ee60d 100644
--- a/numpy/ma/tests/test_core.py
+++ b/numpy/ma/tests/test_core.py
@@ -2671,6 +2671,20 @@ class TestMaskedArrayMethods(TestCase):
         assert_array_equal(x, [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, ])
         assert_equal(x.mask, [1, 0, 0, 0, 1, 1, 0, 0, 0, 0])
 
+    def test_put_nomask(self):
+        # GitHub issue 6425
+        x = zeros(10)
+        z = array([3., -1.], mask=[False, True])
+
+        x.put([1, 2], z)
+        self.assertTrue(x[0] is not masked)
+        assert_equal(x[0], 0)
+        self.assertTrue(x[1] is not masked)
+        assert_equal(x[1], 3)
+        self.assertTrue(x[2] is masked)
+        self.assertTrue(x[3] is not masked)
+        assert_equal(x[3], 0)
+
     def test_put_hardmask(self):
         # Tests put on hardmask
         d = arange(5)