BUG: Fix crash when calling savetxt on a padded array

As a general rule, _every_ use of `.descr` is broken.

Fixes #13297

2 files changed, 12 insertions, 2 deletions

diff --git a/numpy/lib/npyio.py b/numpy/lib/npyio.py
index d702859fa..beeba1334 100644
--- a/numpy/lib/npyio.py
+++ b/numpy/lib/npyio.py
@@ -1379,7 +1379,7 @@ def savetxt(fname, X, fmt='%.18e', delimiter=' ', newline='\n', header='',
 
             # Complex dtype -- each field indicates a separate column
             else:
-                ncol = len(X.dtype.descr)
+                ncol = len(X.dtype.names)
         else:
             ncol = X.shape[1]
 
diff --git a/numpy/lib/tests/test_io.py b/numpy/lib/tests/test_io.py
index 7ef25538b..fc0f988cd 100644
--- a/numpy/lib/tests/test_io.py
+++ b/numpy/lib/tests/test_io.py
@@ -347,13 +347,23 @@ class TestSaveTxt(object):
         assert_raises(ValueError, np.savetxt, c, np.array(1))
         assert_raises(ValueError, np.savetxt, c, np.array([[[1], [2]]]))
 
-    def test_record(self):
+    def test_structured(self):
         a = np.array([(1, 2), (3, 4)], dtype=[('x', 'i4'), ('y', 'i4')])
         c = BytesIO()
         np.savetxt(c, a, fmt='%d')
         c.seek(0)
         assert_equal(c.readlines(), [b'1 2\n', b'3 4\n'])
 
+    def test_structured_padded(self):
+        # gh-13297
+        a = np.array([(1, 2, 3),(4, 5, 6)], dtype=[
+            ('foo', 'i4'), ('bar', 'i4'), ('baz', 'i4')
+        ])
+        c = BytesIO()
+        c.seek(0)
+        np.savetxt(c, a[['foo', 'baz']])
+        assert_equal(c.readlines(), [b'1 3\n', b'4 6\n'])
+
     @pytest.mark.skipif(Path is None, reason="No pathlib.Path")
     def test_multifield_view(self):
         a = np.ones(1, dtype=[('x', 'i4'), ('y', 'i4'), ('z', 'f4')])