From 6386fdb247a409f757fed3ab7026585fd0d2aa3d Mon Sep 17 00:00:00 2001
From: Allan Haldane <allan.haldane@gmail.com>
Date: Sun, 18 Nov 2018 01:37:34 -0500
Subject: [PATCH] BUG: multifield-view of MaskedArray gets bad fill_value

Fixes #10483
---
 numpy/ma/core.py            | 14 ++++++++------
 numpy/ma/tests/test_core.py | 11 +++++++++++
 2 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/numpy/ma/core.py b/numpy/ma/core.py
index 9ee44e9ff61b..4e646981204c 100644
--- a/numpy/ma/core.py
+++ b/numpy/ma/core.py
@@ -449,17 +449,15 @@ def _check_fill_value(fill_value, ndtype):
 
     """
     ndtype = np.dtype(ndtype)
-    fields = ndtype.fields
     if fill_value is None:
         fill_value = default_fill_value(ndtype)
-    elif fields:
-        fdtype = [(_[0], _[1]) for _ in ndtype.descr]
+    elif ndtype.names is not None:
         if isinstance(fill_value, (ndarray, np.void)):
             try:
-                fill_value = np.array(fill_value, copy=False, dtype=fdtype)
+                fill_value = np.array(fill_value, copy=False, dtype=ndtype)
             except ValueError:
                 err_msg = "Unable to transform %s to dtype %s"
-                raise ValueError(err_msg % (fill_value, fdtype))
+                raise ValueError(err_msg % (fill_value, ndtype))
         else:
             fill_value = np.asarray(fill_value, dtype=object)
             fill_value = np.array(_recursive_set_fill_value(fill_value, ndtype),
@@ -780,6 +778,10 @@ def fix_invalid(a, mask=nomask, copy=True, fill_value=None):
     a._data[invalid] = fill_value
     return a
 
+def is_string_or_list_of_strings(val):
+    return (isinstance(val, basestring) or
+            (isinstance(val, list) and
+             builtins.all(isinstance(s, basestring) for s in val)))
 
 ###############################################################################
 #                                  Ufuncs                                     #
@@ -3245,7 +3247,7 @@ def _scalar_heuristic(arr, elem):
             # Inherit attributes from self
             dout._update_from(self)
             # Check the fill_value
-            if isinstance(indx, basestring):
+            if is_string_or_list_of_strings(indx):
                 if self._fill_value is not None:
                     dout._fill_value = self._fill_value[indx]
 
diff --git a/numpy/ma/tests/test_core.py b/numpy/ma/tests/test_core.py
index 8a015e609341..82d7ee960ef1 100644
--- a/numpy/ma/tests/test_core.py
+++ b/numpy/ma/tests/test_core.py
@@ -2029,6 +2029,17 @@ def test_fillvalue(self):
         assert_equal(x.fill_value, 999.)
         assert_equal(x._fill_value, np.array(999.))
 
+    def test_subarray_fillvalue(self):
+        # gh-10483   test multi-field index fill value
+        fields = array([(1, 1, 1)],
+                      dtype=[('i', int), ('s', '|S8'), ('f', float)])
+        with suppress_warnings() as sup:
+            sup.filter(FutureWarning, "Numpy has detected")
+            subfields = fields[['i', 'f']]
+            assert_equal(tuple(subfields.fill_value), (999999, 1.e+20))
+            # test comparison does not raise:
+            subfields[1:] == subfields[:-1]
+
     def test_fillvalue_exotic_dtype(self):
         # Tests yet more exotic flexible dtypes
         _check_fill_value = np.ma.core._check_fill_value