Python排序学生课程的嵌套列表

我是python新手,我很难完成这段代码。有了数据表和给定的代码,我如何制作一个代码来创建每个科目的嵌套列表,参加人数,该科目的平均成绩?输出应如下所示:

[["Physics", 3, 6.0], ["PC", 4, 8.25], ....]

data_list =
 ["John", "Physics", 5], ["John", "PC", 7], ["John", "Math", 8], 
 ["Mary", "Physics", 6], ["Mary", "PC", 10], ["Mary", "Algebra", 7], 
 ["Helen", "Physics", 7], ["Helen","PC", 6], ["Helen", "Algebra", 8], 
 ["Helen", "Analysis", 10], ["Bill", "PC", 10], ["Bill", "Analysis", 6], 
 ["Bill", "Math", 8], ["Bill", "Biology", 6], ["Michael", "Analysis", 10]
]

def groupby(data, index, category):
    """Sort list of records by index and category
    """
    output = []
    indices = []
    for record in data:
        if record[index] not in indices:
            indices.append(record[index])
            output.append([record[index]])
            output[-1].append(record[category])
        else:
            output[indices.index(record[index])].append(record[category])
    return output

# index 0 -> person
# category 1 -> subject
subject_list = groupby(data_list, 0, 1)

# index 0 -> person
# category 2 -> grade
grade_list = groupby(data_list, 0, 2)

# grad_list
[['John', 5, 7, 8],
 ['Mary', 6, 10, 7],
 ['Helen', 7, 6, 8, 10],
 ['Bill', 10, 6, 8, 6],
 ['Michael', 10]]

然后,你可以得到每人所学科目的数量或平均成绩,如下所示:

import statistics

subjects_taken = [len(x) - 1 for x in subject_list]
average_grade = [statistics.mean(x[1:]) for x in grade_list]

persons = [x[0] for x in subject_list]
final_list = list(zip(persons, subjects_taken, average_grade))

# final_list
[('John', 3, 6.666666666666667),
 ('Mary', 3, 7.666666666666667),
 ('Helen', 4, 7.75),
 ('Bill', 4, 7.5),
 ('Michael', 1, 10)]