The sum of rows from the SQLite table in Python

Question

Git: https://github.com/nikitaborisov00/site/tree/main/gpdf

Tell me how to calculate the sum of all grades for each student.

There is a table: with columns (lesson, teacher, student, grade, total, date).

Here is the code creating the model:

migrations.CreateModel(
            name='Grade',
            fields=[
                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
                ('grades', models.IntegerField(default=0, verbose_name='Оценка')),
                ('key', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to='indexing.lecture', verbose_name='За занятие')),
                ('key_to_student', models.ManyToManyField(to='indexing.students', verbose_name='Студентам')),
                ('teacher', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to=settings.AUTH_USER_MODEL, verbose_name='Учитель')),
            ],
            options={
                'verbose_name': 'Оценка',
                'verbose_name_plural': 'Оценки',
            },
        ),

A piece of code from an html file, table output:

 <tbody>
                            {% for row in table %}
                                {% for student in row.key_to_student.all %}
                                    <tr>
                                        <td>{{ student.full_name }}</td>
                                        <td>{{ row.key.title }}</td>
                                        <td>{{ row.teacher.get_full_name }}</td>
                                        {% if row.grades == 0 %}
                                            <td>Пропуск</td>
                                        {% else %}
                                            <td id="value">{{ row.grades }}</td>
                                        {% endif %}
                                        <td>
                                            *<script type="text/javascript">
                                                    let sum = 0;
                                                    for (let i = 1; i <= n; i++) {
                                                        sum += document.getElementById("value");
                                                    document.write(sum);
                                            </script>*
                                        </td>
                                        <td>{{ row.key.date }}</td>
                                        
                                </tr>
                                {% endfor %}
                            {% endfor %}
                            </tbody>