Merge branch 'main' into fix-issue-61221

Author: gsmll

pandas/_libs/lib.pyx

@@ -777,7 +777,10 @@ cpdef ndarray[object] ensure_string_array(
             return out
         arr = arr.to_numpy(dtype=object)
     elif not util.is_array(arr):
-        arr = np.array(arr, dtype="object")
+        # GH#61155: Guarantee a 1-d result when array is a list of lists
+        input_arr = arr
+        arr = np.empty(len(arr), dtype="object")
+        arr[:] = input_arr
 
     result = np.asarray(arr, dtype="object")
 

pandas/tests/libs/test_lib.py

@@ -297,3 +297,13 @@ def test_ensure_string_array_copy():
     assert not np.shares_memory(arr, result)
     assert arr[1] is None
     assert result[1] is np.nan
+
+
+def test_ensure_string_array_list_of_lists():
+    # GH#61155: ensure list of lists doesn't get converted to string
+    arr = [list("test"), list("word")]
+    result = lib.ensure_string_array(arr)
+
+    # Each item in result should still be a list, not a stringified version
+    expected = np.array(["['t', 'e', 's', 't']", "['w', 'o', 'r', 'd']"], dtype=object)
+    tm.assert_numpy_array_equal(result, expected)