BUG: Further fixes to record and recarray getitem/getattr

This is a followup to PR #5505, which didn't go quite far
enough.  This fixes two issues in particular:

1) The record class also needs an updated `__getitem__` that works
analogously to its `__getattribute__` so that a nested record is
returned as a `record` object and not a plain `np.void`.  In other
words the old behavior is:

```python
>>> rec = np.rec.array([('abc ', (1,1), 1), ('abc', (2,3), 1)],
...       dtype=[('foo', 'S4'), ('bar', [('A', int), ('B', int)]),
('baz', int)])
>>> rec[0].bar
(1, 1)
>>> type(rec[0].bar)
<class 'numpy.record'>
>>> type(rec[0]['bar'])
<type 'numpy.void'>
```

demonstrated inconsistency between `.bar` and `['bar']` on the record
object.  The new behavior is:

```python
>>> type(rec[0]['bar'])
<class 'numpy.record'>
```

2) The second issue is more subtle.  The fix to #5505 used the
`obj.dtype.descr` attribute to create a new dtype of type `record`.
However, this does not recreate the correct type if the fields are
not aligned.  To demonstrate:

```python
>>> dt = np.dtype({'C': ('S5', 0), 'D': ('S5', 6)})
>>> dt.fields
dict_proxy({'C': (dtype('S5'), 0), 'D': (dtype('S5'), 6)})
>>> dt.descr
[('C', '|S5'), ('', '|V1'), ('D', '|S5')]
>>> new_dt = np.dtype((np.record, dt.descr))
>>> new_dt
dtype((numpy.record, [('C', 'S5'), ('f1', 'V1'), ('D', 'S5')]))
>>> new_dt.fields
dict_proxy({'f1': (dtype('V1'), 5), 'C': (dtype('S5'), 0), 'D':
(dtype('S5'), 6)})
```

Using the `fields` dict to construct the new type reconstructs the
correct type with the correct offsets:

```python
>>> new_dt2 = np.dtype((np.record, dt.fields))
>>> new_dt2.fields
dict_proxy({'C': (dtype('S5'), 0), 'D': (dtype('S5'), 6)})
```

(Note: This is based on #5920 for convenience, but I could decouple
the changes if that's preferable.)

2 files changed, 28 insertions, 6 deletions

diff --git a/numpy/core/records.py b/numpy/core/records.py
index 243645436..b1ea176e4 100644
--- a/numpy/core/records.py
+++ b/numpy/core/records.py
@@ -245,13 +245,12 @@ class record(nt.void):
                 #happens if field is Object type
                 return obj
             if dt.fields:
-                return obj.view((record, obj.dtype.descr))
+                return obj.view((self.__class__, obj.dtype.fields))
             return obj
         else:
             raise AttributeError("'record' object has no "
                     "attribute '%s'" % attr)
 
-
     def __setattr__(self, attr, val):
         if attr in ['setfield', 'getfield', 'dtype']:
             raise AttributeError("Cannot set '%s' attribute" % attr)
@@ -266,6 +265,16 @@ class record(nt.void):
                 raise AttributeError("'record' object has no "
                         "attribute '%s'" % attr)
 
+    def __getitem__(self, indx):
+        obj = nt.void.__getitem__(self, indx)
+
+        # copy behavior of record.__getattribute__,
+        if isinstance(obj, nt.void) and obj.dtype.fields:
+            return obj.view((self.__class__, obj.dtype.fields))
+        else:
+            # return a single element
+            return obj
+
     def pprint(self):
         """Pretty-print all fields."""
         # pretty-print all fields
@@ -438,7 +447,7 @@ class recarray(ndarray):
         # to preserve numpy.record type if present), since nested structured
         # fields do not inherit type.
         if obj.dtype.fields:
-            return obj.view(dtype=(self.dtype.type, obj.dtype.descr))
+            return obj.view(dtype=(self.dtype.type, obj.dtype.fields))
         else:
             return obj.view(ndarray)
 
@@ -478,7 +487,7 @@ class recarray(ndarray):
         # we might also be returning a single element
         if isinstance(obj, ndarray):
             if obj.dtype.fields:
-                return obj.view(dtype=(self.dtype.type, obj.dtype.descr))
+                return obj.view(dtype=(self.dtype.type, obj.dtype.fields))
             else:
                 return obj.view(type=ndarray)
         else:
diff --git a/numpy/core/tests/test_records.py b/numpy/core/tests/test_records.py
index a7895a30a..2f86b7ccb 100644
--- a/numpy/core/tests/test_records.py
+++ b/numpy/core/tests/test_records.py
@@ -149,19 +149,32 @@ class TestFromrecords(TestCase):
         assert_equal(a.foo[0] == a.foo[1], False)
 
     def test_recarray_returntypes(self):
-        a = np.rec.array([('abc ', (1,1), 1), ('abc', (2,3), 1)],
+        qux_fields = {'C': (np.dtype('S5'), 0), 'D': (np.dtype('S5'), 6)}
+        a = np.rec.array([('abc ', (1,1), 1, ('abcde', 'fgehi')),
+                          ('abc', (2,3), 1, ('abcde', 'jklmn'))],
                          dtype=[('foo', 'S4'),
                                 ('bar', [('A', int), ('B', int)]),
-                                ('baz', int)])
+                                ('baz', int), ('qux', qux_fields)])
         assert_equal(type(a.foo), np.ndarray)
         assert_equal(type(a['foo']), np.ndarray)
         assert_equal(type(a.bar), np.recarray)
         assert_equal(type(a['bar']), np.recarray)
         assert_equal(a.bar.dtype.type, np.record)
+        assert_equal(type(a['qux']), np.recarray)
+        assert_equal(a.qux.dtype.type, np.record)
+        assert_equal(dict(a.qux.dtype.fields), qux_fields)
         assert_equal(type(a.baz), np.ndarray)
         assert_equal(type(a['baz']), np.ndarray)
         assert_equal(type(a[0].bar), np.record)
+        assert_equal(type(a[0]['bar']), np.record)
         assert_equal(a[0].bar.A, 1)
+        assert_equal(a[0].bar['A'], 1)
+        assert_equal(a[0]['bar'].A, 1)
+        assert_equal(a[0]['bar']['A'], 1)
+        assert_equal(a[0].qux.D, asbytes('fgehi'))
+        assert_equal(a[0].qux['D'], asbytes('fgehi'))
+        assert_equal(a[0]['qux'].D, asbytes('fgehi'))
+        assert_equal(a[0]['qux']['D'], asbytes('fgehi'))
 
 
 class TestRecord(TestCase):