Refactor expression handling in DataFrame to improve type checking and error handling

Author: kosiew

python/datafusion/dataframe.py

@@ -478,15 +478,14 @@ def _simplify_expression(
         ) -> list[expr_internal.Expr]:
             expr_list = []
             for expr in exprs:
-                if isinstance(expr, Expr):
-                    expr_list.append(expr.expr)
-                elif isinstance(expr, Iterable) and not isinstance(expr, (str, Expr)):
-                    for inner_expr in expr:
-                        if not isinstance(inner_expr, Expr):
-                            raise TypeError(_EXPR_TYPE_ERROR)
-                        expr_list.append(inner_expr.expr)
-                else:
+                if isinstance(expr, str):
                     raise TypeError(_EXPR_TYPE_ERROR)
+                if isinstance(expr, Iterable) and not isinstance(expr, Expr):
+                    if any(not isinstance(inner_expr, Expr) for inner_expr in expr):
+                        raise TypeError(_EXPR_TYPE_ERROR)
+                elif not isinstance(expr, Expr):
+                    raise TypeError(_EXPR_TYPE_ERROR)
+                expr_list.extend(expr_list_to_raw_expr_list(expr))
             if named_exprs:
                 for alias, expr in named_exprs.items():
                     if not isinstance(expr, Expr):