可变对象传入set

set=([1,2,3]), 其中（[ ]）只是set的表现形式，并非把list放入set中

>>> s1=set([1,2,3])
>>> L
[1, 2, 3]
>>> s1
{1, 2, 3}
>>> s1(L)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'set' object is not callable