任意输入含加减乘除乘方开方的文本数学表达式文本，自动计算结果

def eval_formula(formula):
    import math
    import ast
    import operator as op

    operators = {ast.Add: op.add, ast.Sub: op.sub, ast.Mult: op.mul,
                 ast.Div: op.truediv, ast.Pow: op.pow, ast.BitXor: op.xor,
                 ast.USub: op.neg}
    def eval_expr(node):
        if isinstance(node, ast.Num):  # <number>
            return node.n
        elif isinstance(node, ast.operator):  # <operator>
            return operators[type(node)]
        elif isinstance(node, ast.UnaryOp):  # <unaryop> <expr>
            return eval_expr(node.op)(eval_expr(node.operand))
        elif isinstance(node, ast.BinOp):  # <expr> <operator> <expr>
            return eval_expr(node.op)(eval_expr(node.left), eval