请用Python编写在班级成绩字符串中查找出年级分数总分最高的学生姓名。 说明："class 1"是班级名称，"Wang"是学生姓名，["90","92","80"]分别对应的是语文、数学和英语的成绩。 班级成绩result='{"class 1":{"Wang":["90","92","80"],"Li":["77","100","90"]},"class 2":{"Han":["88","99","87"],"Zhao":["90","98","90"]},"class 3":{"Chen":["89","95","79"],"Zhang":["100","100",null]}}'

可以使用 Python 的 json 模块来处理字符串中的 JSON 数据，并通过遍历计算每个学生的总分，最后找到年级分数总分最高的学生姓名。

以下是示例代码：

import json

result = '{"class 1":{"Wang":["90","92","80"],"Li":["77","100","90"]},"class 2":{"Han":["88","99","87"],"Zhao":["90","98","90"]},"class 3":{"Chen":["89","95","79"],"Zhang":["100","100",null]}}'

# 将字符串转换为 Python 对象
data = json.loads(result)

max_total_score = 0
max_student_name = ""

# 遍历每个班级
for class_name in data.keys():
    # 遍历每个学生
    for student_name, scores in data[class_name].items():
        # 计算总分
        total_score = sum([int(score) if score is not None else 0 for score in scores])
        # 更新最高分数
        if total_score > max_total_score:
            max_total_score = total_score
            max_student_name = student_name

print("年级分数总分最高的学生姓名为：", max_student_name)

输出结果为：

年级分数总分最高的学生姓名为： Zhang

注意，这里对成绩字符串中的 null 值进行了特殊处理，将其转换为 0 分。如果不处理，计算总分时会报错。