python中怎样画分段函数?

import numpy as np

import matplotlib.pyplot as plt

def sgn(x):

    if x > 0:

        return 1

    elif x < 0:

        return -1

    else:

        return 0

t = np.arange(0, 1, 0.01)

y = []

for i in t:

    y_1 = 4 * np.sin(4 * np.pi * i) - sgn(i - 0.3) - sgn(0.72 - i)

    y.append(y_1)

plt.plot(t, y)

plt.xlabel("t")

plt.ylabel("y")

plt.title("Heavsine")

plt.show()