Euler

import matplotlib.pyplot as plt

x, y = 0.0, 1.0
tarX = 10.0
buchang = 0.1
X, Y = [x], [y]

def f(x:float, y:float):
    return y - 2 * x / y

while x <= tarX:
    k1 = f(x, y)
    k2 = f(x + buchang, y + k1 * buchang)
    y = y + 0.5 * (k1 + k2) * buchang
    x = x + buchang


    X.append(x)
    Y.append(y)
plt.plot(X, Y)
plt.show()