Python:确定一个字符串是否包含数学

给定这些字符串:

"1 + 2" 
"apple,pear" 

如何使用 Python 3(.5) 确定第一个字符串包含数学问题且没有其他内容，而第二个字符串不包含？

请您参考如下方法:

这里有一个方法:

import ast 
 
UNARY_OPS = (ast.UAdd, ast.USub) 
BINARY_OPS = (ast.Add, ast.Sub, ast.Mult, ast.Div, ast.Mod) 
 
def is_arithmetic(s): 
    def _is_arithmetic(node): 
        if isinstance(node, ast.Num): 
            return True 
        elif isinstance(node, ast.Expression): 
            return _is_arithmetic(node.body) 
        elif isinstance(node, ast.UnaryOp): 
            valid_op = isinstance(node.op, UNARY_OPS) 
            return valid_op and _is_arithmetic(node.operand) 
        elif isinstance(node, ast.BinOp): 
            valid_op = isinstance(node.op, BINARY_OPS) 
            return valid_op and _is_arithmetic(node.left) and _is_arithmetic(node.right) 
        else: 
            raise ValueError('Unsupported type {}'.format(node)) 
 
    try: 
        return _is_arithmetic(ast.parse(s, mode='eval')) 
    except (SyntaxError, ValueError): 
        return False