"""Tool: calculator — Evaluate a mathematical expression safely."""
import ast, operator as op
_OPS = {ast.Add: op.add, ast.Sub: op.sub, ast.Mult: op.mul, ast.Div: op.truediv,
        ast.Pow: op.pow, ast.Mod: op.mod, ast.USub: op.neg, ast.UAdd: op.pos, ast.FloorDiv: op.floordiv}
def calculator(expression: str):
    """Evaluate a mathematical expression. Returns float."""
    def _eval(node):
        if isinstance(node, ast.Num): return node.n
        if isinstance(node, ast.Constant): return node.value
        if isinstance(node, ast.BinOp): return _OPS[type(node.op)](_eval(node.left), _eval(node.right))
        if isinstance(node, ast.UnaryOp): return _OPS[type(node.op)](_eval(node.operand))
        raise ValueError(f"Unsupported: {type(node).__name__}")
    tree = ast.parse(expression, mode="eval")
    return float(_eval(tree.body))