python提取json字符串的值

 json_str={
     "actor":"邓超",
     "age":35,
     "book":[
         "英语",
         "数学",
         "美术"
     ],
     "children":[
         {
             "name":"等等",
             "age":7,
             "sex":"male"
         },
         {
             "name":"花花",
             "age":3,
             "sex":"female"
         }
     ]
 }

 #获取actor 的值
 actor=json_str['actor']
 #获取 book 的第二个值
 book_2=json_str['book'][1]
 #获取第二个孩子的性别
 sex2=json_str['children'][1]['sex']