HKUDS/Vibe-Trading · error · ValueError

disallowed element in expression: {type(node).__name__}

Error message

disallowed element in expression: {type(node).__name__}

What it means

The recursive evaluator _eval_arith_node only accepts Constant, BinOp, and UnaryOp nodes; anything else (Name, Call, Attribute, Compare, etc.) hits the terminal raise. This prevents name lookups and function calls, keeping evaluation side-effect free and exact. The message reports the disallowed AST node type name.

Source

Thrown at agent/src/tools/financial_rigor_tool.py:111

    Raises:
        ValueError: If the node is not a supported numeric/arithmetic form.
    """
    if isinstance(node, ast.Constant):
        # bool is a subclass of int — reject it explicitly.
        if isinstance(node.value, bool) or not isinstance(node.value, (int, float)):
            raise ValueError("only numeric constants are allowed")
        return _exact(node.value)
    if isinstance(node, ast.BinOp):
        op_fn = _AST_BINOPS.get(type(node.op))
        if op_fn is None:
            raise ValueError(f"unsupported operator: {type(node.op).__name__}")
        return op_fn(_eval_arith_node(node.left), _eval_arith_node(node.right))
    if isinstance(node, ast.UnaryOp):
        op_fn = _AST_UNARYOPS.get(type(node.op))
        if op_fn is None:
            raise ValueError(f"unsupported unary operator: {type(node.op).__name__}")
        return op_fn(_eval_arith_node(node.operand))
    raise ValueError(f"disallowed element in expression: {type(node).__name__}")


def _safe_arith(expr: str) -> Decimal:
    """Evaluate a numeric arithmetic expression in the exact-Decimal domain.

    The expression is parsed and evaluated recursively with Decimal arithmetic,
    so ``0.1 + 0.2`` is exactly ``0.3`` — no IEEE-754 drift, and no ``eval``.
    Only numbers and the operators ``+ - * /`` (with optional unary sign) are
    permitted; any other AST node raises ``ValueError``.

    Args:
        expr: Arithmetic expression string, e.g. ``"510 * 9.11e9"``.

    Returns:
        The exact Decimal result.

    Raises:
        ValueError: If the expression is malformed or contains a disallowed

View on GitHub (pinned to 80ffdda44c)

Solutions

1. Inline all values as numeric literals
2. Replace function calls with equivalent arithmetic
3. If variables are needed, add a controlled name-binding map to the evaluator rather than allowing arbitrary Names

Example fix

// before
_safe_arith("abs(-3) + 2")
// after
_safe_arith("3 + 2")

import ast
expr = "abs(-1)"
tree = ast.parse(expr, mode="eval")
allowed = (ast.Constant, ast.BinOp, ast.UnaryOp, ast.UAdd, ast.USub,
           ast.Add, ast.Sub, ast.Mult, ast.Div, ast.FloorDiv, ast.Mod, ast.Pow)
assert all(isinstance(n, allowed) for n in ast.walk(tree)), "disallowed node present"

def is_pure_arith(expr: str) -> bool:
    import ast
    try:
        tree = ast.parse(expr, mode="eval")
    except SyntaxError:
        return False
    allowed = (ast.Expression, ast.Constant, ast.BinOp, ast.UnaryOp,
               ast.Load, ast.UAdd, ast.USub, ast.Add, ast.Sub, ast.Mult,
               ast.Div, ast.FloorDiv, ast.Mod, ast.Pow)
    return all(isinstance(n, allowed) for n in ast.walk(tree))

try:
    value = _safe_arith(expr)
except ValueError as e:
    if "disallowed element" in str(e):
        value = None  # or fall back to shunting-yard on a numeric tokenizer
    else:
        raise

When it happens

Trigger: Expressions referencing variables ('pi * 2'), function calls ('abs(-1)'), comparisons ('1 < 2'), tuples, f-strings, or any construct beyond literal arithmetic.

Common situations: LLM tool calls that include helper functions or variable references; users expecting the calculator to accept full Python.

Related errors

• unsupported operator: {type(node.op).__name__}
• unsupported unary operator: {type(node.op).__name__}
• only numeric constants are allowed
• malformed expression: {exc}
• artifact_path escapes the current run_dir

AI-assisted analysis of HKUDS/Vibe-Trading@80ffdda44c (2026-08-28). Data as JSON: /api/errors/9ff489da31eecb32. Report an issue: GitHub.