import numpy as np
import matplotlib.pyplot as plt

x = np.linspace(-np.pi, np.pi, 1000)
cosy = np.cos(x)
siny = np.sin(x)

plt.xlim(min(x), max(x))
plt.ylim(min(cosy), max(cosy)+0.5)
plt.plot(x, cosy)
plt.plot(x, siny)
# 设置坐标刻度
plt.xticks([-np.pi, -np.pi/2, 0, np.pi/2, np.pi *3/4, np.pi],)

# 设置坐标轴
ax = plt.gca()
ax.spines['left'].set_position(('data', 0))
ax.spines['bottom'].set_position(('data', 0))
ax.spines['right'].set_position(('data', 0))
ax.spines['top'].set_position(('data', 0))
plt.show()