BUG: Change ndarray.__new__ to allow zero-width data types, and in particular without converting zero-width strings to a one-width string dtype.

ndarray.__new__, being relatively low-level, should not be mangling the requested dtype when creating an array.

See #6430

2 files changed, 15 insertions, 14 deletions

diff --git a/numpy/core/src/multiarray/arrayobject.c b/numpy/core/src/multiarray/arrayobject.c
index 277c6517c..c21bcaecf 100644
--- a/numpy/core/src/multiarray/arrayobject.c
+++ b/numpy/core/src/multiarray/arrayobject.c
@@ -1652,11 +1652,6 @@ array_new(PyTypeObject *subtype, PyObject *args, PyObject *kwds)
     }
 
     itemsize = descr->elsize;
-    if (itemsize == 0) {
-        PyErr_SetString(PyExc_ValueError,
-                        "data-type with unspecified variable length");
-        goto fail;
-    }
 
     if (strides.ptr != NULL) {
         npy_intp nb, off;
@@ -1690,10 +1685,11 @@ array_new(PyTypeObject *subtype, PyObject *args, PyObject *kwds)
 
     if (buffer.ptr == NULL) {
         ret = (PyArrayObject *)
-            PyArray_NewFromDescr(subtype, descr,
-                                 (int)dims.len,
-                                 dims.ptr,
-                                 strides.ptr, NULL, is_f_order, NULL);
+            PyArray_NewFromDescr_int(subtype, descr,
+                                     (int)dims.len,
+                                     dims.ptr,
+                                     strides.ptr, NULL, is_f_order, NULL,
+                                     0, 1);
         if (ret == NULL) {
             descr = NULL;
             goto fail;
@@ -1726,11 +1722,11 @@ array_new(PyTypeObject *subtype, PyObject *args, PyObject *kwds)
             buffer.flags |= NPY_ARRAY_F_CONTIGUOUS;
         }
         ret = (PyArrayObject *)\
-            PyArray_NewFromDescr(subtype, descr,
-                                 dims.len, dims.ptr,
-                                 strides.ptr,
-                                 offset + (char *)buffer.ptr,
-                                 buffer.flags, NULL);
+            PyArray_NewFromDescr_int(subtype, descr,
+                                     dims.len, dims.ptr,
+                                     strides.ptr,
+                                     offset + (char *)buffer.ptr,
+                                     buffer.flags, NULL, 0, 1);
         if (ret == NULL) {
             descr = NULL;
             goto fail;
diff --git a/numpy/core/tests/test_multiarray.py b/numpy/core/tests/test_multiarray.py
index 66f6e23cb..9d7c53e67 100644
--- a/numpy/core/tests/test_multiarray.py
+++ b/numpy/core/tests/test_multiarray.py
@@ -947,6 +947,11 @@ class TestStructured(TestCase):
         assert_equal(x['S'], [b'', b'', b'', b''])
         assert_equal(x['I'], [0, 0, 0, 0])
 
+        # Allow zero-width dtypes in ndarray constructor
+        y = np.ndarray(4, dtype=x['S'].dtype)
+        assert_equal(y.itemsize, 0)
+        assert_equal(x['S'], y)
+
         # More tests for indexing an array with zero-width fields
         assert_equal(np.zeros(4, dtype=[('a', 'S0,S0'),
                                         ('b', 'u1')])['a'].itemsize, 0)