python画图

x = np.arange(0., np.e, 0.01)
y1 = np.exp(-x)
y2 = np.log(x)

fig = plt.figure()

ax1 = fig.add_subplot(111)
ax1.plot(x, y1)
ax1.set_ylabel(‘Y values for exp(-x)‘)
ax1.set_title("Double Y axis")

ax2 = ax1.twinx()  # this is the important function
ax2.plot(x, y2, ‘r‘)
ax2.set_xlim([0, np.e])
ax2.set_ylabel(‘Y values for ln(x)‘)
ax2.set_xlabel(‘Same X for both exp(-x) and ln(x)‘)

plt.show()

def sgn(value):
    if value < 4:
        return 20
    else:
        return 15
plt.figure(figsize=(6,4))
x = np.linspace(0, 8, 100)
y = np.array([])
for v in x:
    y = np.append(y,np.linspace(sgn(v),sgn(v),1))
l=plt.plot(x,y,‘b‘,label=‘type‘)
plt.legend()
plt.show()