Matplotlib CW

import matplotlib.pyplot as plt
import numpy as np

grades = [3, 8, 1, 4, 10, 9]
week = list(range(1, len(grades) + 1))

max_grade = max(grades)
min_grade = min(grades)

min_index = grades.index(min(grades))
plt.plot(
    week[:min_index + 1], grades[:min_index + 1], '-.k',
    week[min_index:], grades[min_index:], ':k'
)
plt.plot(week[grades.index(max(grades))], max_grade, marker = "*")
plt.plot(week[grades.index(min(grades))], min_grade, marker = "^")

threshold = 7
for x in grades:
    if threshold < x and x < max_grade:
        plt.plot(week[grades.index(x)], x, marker='o')
    elif min_grade < x and x < threshold:
        plt.plot(week[grades.index(x)], x, marker='s')

plt.show()