fix(python): normalize merge insert column lists

python/python/lancedb/table.py

@@ -1346,7 +1346,7 @@ class Table(ABC):
         2  3  y
         3  4  z
         """  # noqa: E501
-        on = [on] if isinstance(on, str) else list(iter(on))
+        on = [on] if isinstance(on, str) else list(on)
 
         return LanceMergeInsertBuilder(self, on)
 
@@ -5236,7 +5236,7 @@ class AsyncTable:
         2  3  y
         3  4  z
         """  # noqa: E501
-        on = [on] if isinstance(on, str) else list(iter(on))
+        on = [on] if isinstance(on, str) else list(on)
 
         return LanceMergeInsertBuilder(self, on)
 

python/python/tests/test_table.py

@@ -2265,6 +2265,31 @@ def test_update_types(mem_db: DBConnection):
     assert actual == expected
 
 
+def test_merge_insert_accepts_column_list(mem_db: DBConnection):
+    table = mem_db.create_table(
+        "my_table",
+        data=pa.table({"a": [1], "b": [2]}),
+    )
+
+    builder = table.merge_insert(["a", "b"])
+
+    assert builder._on == ["a", "b"]
+
+
+@pytest.mark.asyncio
+async def test_merge_insert_accepts_column_list_async(
+    mem_db_async: AsyncConnection,
+):
+    table = await mem_db_async.create_table(
+        "my_table",
+        data=pa.table({"a": [1], "b": [2]}),
+    )
+
+    builder = table.merge_insert(["a", "b"])
+
+    assert builder._on == ["a", "b"]
+
+
 def test_merge_insert(mem_db: DBConnection):
     table = mem_db.create_table(
         "my_table",