import scipy.signal
b = sp.signal.firwin(80, 0.5, window=('kaiser', 8))
h, w = sp.signal.freqz(b)

import matplotlib.pyplot as plt
fig = plt.figure()
plt.title('Digital filter frequency response')
ax1 = fig.add_subplot(111)

plt.semilogy(h, np.abs(w), 'b')
plt.ylabel('Amplitude (dB)', color='b')
plt.xlabel('Frequency (rad/sample)')
plt.grid()
plt.legend()

ax2 = ax1.twinx()
angles = np.unwrap(np.angle(w))
plt.plot(h, angles, 'g')
plt.ylabel('Angle (radians)', color='g')
plt.show()