BUG: fix deepcopying StringDType arrays (#28643)

Fixes #28609
numpy · charris · Apr 5, 2025 · Apr 4, 2025 · Apr 5, 2025 · 3c831617b5778038613c9f9d1672948e534815f9
commit 3c831617b5778038613c9f9d1672948e534815f9
diff --git a/numpy/_core/src/multiarray/methods.c b/numpy/_core/src/multiarray/methods.c
@@ -1605,7 +1605,7 @@ _deepcopy_call(char *iptr, char *optr, PyArray_Descr *dtype,
            }
        }
    }
-    else {
+    else if (PyDataType_ISOBJECT(dtype)) {
        PyObject *itemp, *otemp;
        PyObject *res;
        memcpy(&itemp, iptr, sizeof(itemp));

diff --git a/numpy/_core/tests/test_stringdtype.py b/numpy/_core/tests/test_stringdtype.py
@@ -1,8 +1,9 @@
 import concurrent.futures
+import copy
 import itertools
 import os
-import pickle
 import string
+import pickle
 import sys
 import tempfile

@@ -405,6 +406,13 @@ def test_pickle(dtype, string_list):
    os.remove(f.name)


+def test_stdlib_copy(dtype, string_list):
+    arr = np.array(string_list, dtype=dtype)
+
+    assert_array_equal(copy.copy(arr), arr)
+    assert_array_equal(copy.deepcopy(arr), arr)
+
+
 @pytest.mark.parametrize(
    "strings",
    [
@@ -1728,12 +1736,12 @@ def test_zeros(self):
        assert_array_equal(z, "")

    def test_copy(self):
-        c = self.a.copy()
-        assert_array_equal(self.get_flags(c), self.get_flags(self.a))
-        assert_array_equal(c, self.a)
-        offsets = self.get_view(c)['offset']
-        assert offsets[2] == 1
-        assert offsets[3] == 1 + len(self.s_medium) + self.sizeofstr // 2
+        for c in [self.a.copy(), copy.copy(self.a), copy.deepcopy(self.a)]:
+            assert_array_equal(self.get_flags(c), self.get_flags(self.a))
+            assert_array_equal(c, self.a)
+            offsets = self.get_view(c)['offset']
+            assert offsets[2] == 1
+            assert offsets[3] == 1 + len(self.s_medium) + self.sizeofstr // 2

    def test_arena_use_with_setting(self):
        c = np.zeros_like(self.a)