BUG: recfunctions: Don't return None in place of empty sequences

Replacing empty tuples with `None` is a bad idea, and just results in an API that is hard to consume - especially since the behavior was never documented.

This affects `get_names`, `get_names_flat`, and `get_fieldstructure`.

2 files changed, 27 insertions, 6 deletions

diff --git a/numpy/lib/recfunctions.py b/numpy/lib/recfunctions.py
index fcc0d9a7a..fb0ae5cc3 100644
--- a/numpy/lib/recfunctions.py
+++ b/numpy/lib/recfunctions.py
@@ -132,11 +132,11 @@ def get_names(adtype):
     names = adtype.names
     for name in names:
         current = adtype[name]
-        if current.names:
+        if current.names is not None:
             listnames.append((name, tuple(get_names(current))))
         else:
             listnames.append(name)
-    return tuple(listnames) or None
+    return tuple(listnames)
 
 
 def get_names_flat(adtype):
@@ -165,9 +165,9 @@ def get_names_flat(adtype):
     for name in names:
         listnames.append(name)
         current = adtype[name]
-        if current.names:
+        if current.names is not None:
             listnames.extend(get_names_flat(current))
-    return tuple(listnames) or None
+    return tuple(listnames)
 
 
 def flatten_descr(ndtype):
@@ -263,7 +263,7 @@ def get_fieldstructure(adtype, lastname=None, parents=None,):
     names = adtype.names
     for name in names:
         current = adtype[name]
-        if current.names:
+        if current.names is not None:
             if lastname:
                 parents[name] = [lastname, ]
             else:
@@ -276,7 +276,7 @@ def get_fieldstructure(adtype, lastname=None, parents=None,):
             elif lastname:
                 lastparent = [lastname, ]
             parents[name] = lastparent or []
-    return parents or None
+    return parents
 
 
 def _izip_fields_flat(iterable):
diff --git a/numpy/lib/tests/test_recfunctions.py b/numpy/lib/tests/test_recfunctions.py
index 11f8a5afa..3b972f4b1 100644
--- a/numpy/lib/tests/test_recfunctions.py
+++ b/numpy/lib/tests/test_recfunctions.py
@@ -113,6 +113,14 @@ class TestRecFunctions(object):
         test = get_names(ndtype)
         assert_equal(test, ('a', ('b', ('ba', 'bb'))))
 
+        ndtype = np.dtype([('a', int), ('b', [])])
+        test = get_names(ndtype)
+        assert_equal(test, ('a', ('b', ())))
+
+        ndtype = np.dtype([])
+        test = get_names(ndtype)
+        assert_equal(test, ())
+
     def test_get_names_flat(self):
         # Test get_names_flat
         ndtype = np.dtype([('A', '|S3'), ('B', float)])
@@ -123,6 +131,14 @@ class TestRecFunctions(object):
         test = get_names_flat(ndtype)
         assert_equal(test, ('a', 'b', 'ba', 'bb'))
 
+        ndtype = np.dtype([('a', int), ('b', [])])
+        test = get_names_flat(ndtype)
+        assert_equal(test, ('a', 'b'))
+
+        ndtype = np.dtype([])
+        test = get_names_flat(ndtype)
+        assert_equal(test, ())
+
     def test_get_fieldstructure(self):
         # Test get_fieldstructure
 
@@ -145,6 +161,11 @@ class TestRecFunctions(object):
                    'BBA': ['B', 'BB'], 'BBB': ['B', 'BB']}
         assert_equal(test, control)
 
+        # 0 fields
+        ndtype = np.dtype([])
+        test = get_fieldstructure(ndtype)
+        assert_equal(test, {})
+
     def test_find_duplicates(self):
         # Test find_duplicates
         a = ma.array([(2, (2., 'B')), (1, (2., 'B')), (2, (2., 'B')),