python语句结尾的逗号有什么用？

Question

对于return line, 很不理解。。。
源代码如下：
http://matplotlib.org/example...

"""
A simple example of an animated plot
"""
import numpy as np
import matplotlib.pyplot as plt
import matplotlib.animation as animation

fig, ax = plt.subplots()

x = np.arange(0, 2*np.pi, 0.01)
**line, =** ax.plot(x, np.sin(x))


def animate(i):
    line.set_ydata(np.sin(x + i/10.0))  # update the data
    **return line,**


# Init only required for blitting to give a clean slate.
def init():
    line.set_ydata(np.ma.array(x, mask=True))
    **return line,**

ani = animation.FuncAnimation(fig, animate, np.arange(1, 200), init_func=init,
                              interval=25, blit=True)
plt.show()

Answer 1

def f():
    return 1,
type(f())

试试就知道啦，加一个逗号就是返回tuple了

Answer 2

区分元组和单个值
返回元组，就不能被更改
元组可以参考这个
廖雪峰 元组