BUG: Fixed slicing of chararrays on Python 3.

When taking a slice of a chararray it was calling the rstrip() method
on the resulting slice, resulting in a new array rather than a view
of the original.  This was an unintended consequence of the sq_slice
member of the tp_as_sequence mapping being ignored in Python 3, so
that slice lookups go directly through __getitem__.

Fix test_expandtabs to not make the assumption that rstrip() will be applied twice to a value when using T[x][y] style indexing.

2 files changed, 21 insertions, 2 deletions

diff --git a/numpy/core/defchararray.py b/numpy/core/defchararray.py
index cc6cb5a38..92ea8209c 100644
--- a/numpy/core/defchararray.py
+++ b/numpy/core/defchararray.py
@@ -1849,12 +1849,14 @@ class chararray(ndarray):
 
     def __getitem__(self, obj):
         val = ndarray.__getitem__(self, obj)
-        if issubclass(val.dtype.type, character) and not _len(val) == 0:
+
+        if isinstance(val, character):
             temp = val.rstrip()
             if _len(temp) == 0:
                 val = ''
             else:
                 val = temp
+
         return val
 
     # IMPLEMENTATION NOTE: Most of the methods of this class are
diff --git a/numpy/core/tests/test_defchararray.py b/numpy/core/tests/test_defchararray.py
index 2b45ba4bc..a611f8552 100644
--- a/numpy/core/tests/test_defchararray.py
+++ b/numpy/core/tests/test_defchararray.py
@@ -329,7 +329,7 @@ class TestMethods(TestCase):
 
     def test_expandtabs(self):
         T = self.A.expandtabs()
-        assert_(T[2][0] == asbytes('123      345'))
+        assert_(T[2, 0] == asbytes('123      345 \0'))
 
     def test_join(self):
         if sys.version_info[0] >= 3:
@@ -629,6 +629,23 @@ class TestOperations(TestCase):
                 self.fail("chararray __rmod__ should fail with " \
                           "non-string objects")
 
+    def test_slice(self):
+        """Regression test for https://github.com/numpy/numpy/issues/5982"""
+
+        arr = np.array([['abc ', 'def '], ['geh ', 'ijk ']],
+                       dtype='S4').view(np.chararray)
+        sl1 = arr[:]
+        assert_array_equal(sl1, arr)
+        assert sl1.base is arr
+        assert sl1.base.base is arr.base
+
+        sl2 = arr[:, :]
+        assert_array_equal(sl2, arr)
+        assert sl2.base is arr
+        assert sl2.base.base is arr.base
+
+        assert arr[0, 0] == asbytes('abc')
+
 
 def test_empty_indexing():
     """Regression test for ticket 1948."""