原文：https://stackoverflow.com/questions/21809112/what-does-tuple-and-dict-mean-in-python
*tuple可以理解为把tuple的内容展开
def foo(x, y):
print(x, y)
>>> t = (1, 2)
>>> foo(*t)
1 2**dict可以理解为以key=value的方式展开
def foo(x, y):
print(x, y)
>>> d = {'x':1, 'y':2}
>>> foo(**d)
1 2