feat: enhance ensure_expr_list to treat string-like objects as atomic

Author: kosiew

python/datafusion/expr.py

@@ -261,7 +261,10 @@ def ensure_expr_list(
 
     def _iter(items: Iterable[Expr | Iterable[Expr]]) -> Iterable[expr_internal.Expr]:
         for expr in items:
-            if isinstance(expr, Iterable) and not isinstance(expr, Expr):
+            if isinstance(expr, Iterable) and not isinstance(
+                expr, (Expr, str, bytes, bytearray)
+            ):
+                # Treat string-like objects as atomic to surface standard errors
                 yield from _iter(expr)
             else:
                 yield ensure_expr(expr)

python/tests/test_expr.py

@@ -50,6 +50,7 @@
     TransactionStart,
     Values,
     ensure_expr,
+    ensure_expr_list,
 )
 
 
@@ -890,3 +891,18 @@ def test_ensure_expr():
     assert ensure_expr(e) is e.expr
     with pytest.raises(TypeError, match=re.escape(EXPR_TYPE_ERROR)):
         ensure_expr("a")
+
+
+def test_ensure_expr_list_string():
+    with pytest.raises(TypeError, match=re.escape(EXPR_TYPE_ERROR)):
+        ensure_expr_list("a")
+
+
+def test_ensure_expr_list_bytes():
+    with pytest.raises(TypeError, match=re.escape(EXPR_TYPE_ERROR)):
+        ensure_expr_list(b"a")
+
+
+def test_ensure_expr_list_bytearray():
+    with pytest.raises(TypeError, match=re.escape(EXPR_TYPE_ERROR)):
+        ensure_expr_list(bytearray(b"a"))