allow non-unitary strides when slicing vlen vars

Author: Jeffrey Whitaker

Changelog

@@ -6,6 +6,7 @@
    perform a membership operation on a Dataset (issue #1383)
  * fix type hint for createEnumType (issue #1378)
  * add python 3.13 to windows wheel builds (PR #1377)
+ * allow slicing of vlen and string variables with non-unitary strides (issue #1408).
 
  version 1.7.2 (tag v1.7.2rel)
  =============================

src/netCDF4/_netCDF4.pyx

@@ -5966,10 +5966,10 @@ NC_CHAR).
                         ierr = nc_put_vara(self._grpid, self._varid,
                                            startp, countp, strdata)
                 else:
-                    raise IndexError('strides must all be 1 for string variables')
-                    #with nogil:
-                    #    ierr = nc_put_vars(self._grpid, self._varid,
-                    #                       startp, countp, stridep, strdata)
+                    #raise IndexError('strides must all be 1 for string variables')
+                    with nogil:
+                        ierr = nc_put_vars(self._grpid, self._varid,
+                                           startp, countp, stridep, strdata)
                 _ensure_nc_success(ierr)
                 free(strdata)
             else:
@@ -5995,10 +5995,10 @@ NC_CHAR).
                         ierr = nc_put_vara(self._grpid, self._varid,
                                            startp, countp, vldata)
                 else:
-                    raise IndexError('strides must all be 1 for vlen variables')
-                    #with nogil:
-                    #    ierr = nc_put_vars(self._grpid, self._varid,
-                    #                       startp, countp, stridep, vldata)
+                    #raise IndexError('strides must all be 1 for vlen variables')
+                    with nogil:
+                        ierr = nc_put_vars(self._grpid, self._varid,
+                                           startp, countp, stridep, vldata)
                 _ensure_nc_success(ierr)
                 # free the pointer array.
                 free(vldata)
@@ -6130,10 +6130,10 @@ NC_CHAR).
                         ierr = nc_get_vara(self._grpid, self._varid,
                                            startp, countp, vldata)
                 else:
-                    raise IndexError('strides must all be 1 for vlen variables')
-                    #with nogil:
-                    #    ierr = nc_get_vars(self._grpid, self._varid,
-                    #                       startp, countp, stridep, vldata)
+                    #raise IndexError('strides must all be 1 for vlen variables')
+                    with nogil:
+                        ierr = nc_get_vars(self._grpid, self._varid,
+                                           startp, countp, stridep, vldata)
                 if ierr == NC_EINVALCOORDS:
                     raise IndexError
                 elif ierr != NC_NOERR:

test/test_vlen.py

@@ -76,6 +76,12 @@ def runTest(self):
                 assert_array_equal(data2[j,i], data[j,i])
                 assert datas[j,i] == data2s[j,i]
         assert_array_equal(datas, vs_alt[:])
+        # issue #1408
+        data2a = data2[::2,::2]
+        data2b = v[::2,::2]
+        for i in range(nlons//2):
+            for j in range(nlats//2):
+                assert_array_equal(data2a[j,i], data2b[j,i])
         f.close()