FIX: handle insertion of 0-dim datetime64 arrays into string scalars …

…in np.insert (#29339) - Fix np.insert to correctly convert 0-dim np.datetime64 arrays to strings when inserting into string arrays. This resolves RuntimeError when inserting datetime64 wrapped in 0-d arrays.
numpy · AnkitAhlawat7742 · Jul 22, 2025 · Jul 22, 2025 · Jul 22, 2025 · 73ad033aa1a33e7a87a6a2ac1549be899118f073
commit 73ad033aa1a33e7a87a6a2ac1549be899118f073
diff --git a/numpy/lib/_function_base_impl.py b/numpy/lib/_function_base_impl.py
@@ -5612,7 +5612,14 @@ def insert(arr, obj, values, axis=None):
                              f"with size {N}")
         if (index < 0):
             index += N
-
+        # np.insert fails with datetime64 and string input combination #29339
+        if isinstance(values, np.ndarray):
+            if np.issubdtype(values.dtype, np.datetime64) and \
+            np.issubdtype(arr.dtype, np.str_):
+                if values.ndim == 0:
+                    values = values.item()
+                else:
+                    values = values.astype(str)
         # There are some object array corner cases here, but we cannot avoid
         # that:
         values = array(values, copy=None, ndmin=arr.ndim, dtype=arr.dtype)

diff --git a/numpy/lib/tests/test_function_base.py b/numpy/lib/tests/test_function_base.py
@@ -1344,6 +1344,13 @@ def test_return_type(self):
         res = np.gradient(([1, 2], [2, 3]))
         assert type(res) is tuple
 
+    def test_insert_0d_datetime64_into_string_scalar(self):
+        # np.insert fails with datetime64 and string input combination #29339
+        arr = '5'
+        val_0d = np.array(np.datetime64('2025-10-10'))  # 0-d array
+        result_0d = np.insert(arr, 0, val_0d)
+        expected_0d = np.array(['2025-10-10', '5'], dtype='<U10')
+        assert_array_equal(result_0d, expected_0d)
 
 class TestAngle: