Interactive matplotlib using ipywidgets

I want to implement an interactive plot using Matplotlib and ipywidgets in IPython (python3). So, how I can do this efficiently (change smoothly without delay)? And another question is why this code works?! ``` from ipywidgets import * import numpy as np import matplotlib.pyplot as plt %matplotlib inline x = np.linspace(0, 2 * np.pi) def update(w = 1.0): fig = plt.figure() ax = fig.add_subplot(1, 1, 1) ax.plot(x, np.sin(w * x)) fig.canvas.draw() interact(update); ``` But, this doesn't work?! ``` from ipywidgets import * import numpy as np import matplotlib.pyplot as plt %matplotlib inline x = np.linspace(0, 2 * np.pi) fig = plt.figure() ax = fig.add_subplot(1, 1, 1) line, = ax.plot(x, np.sin(x)) def update(w = 1.0): line.set_ydata(np.sin(w * x)) fig.canvas.draw() interact(update); ```