python多重赋值

多重赋值语句，不是说x=y, y=x+y=y+y,而是把右边的变量赋给临时变量后，再做赋值（In an assignment statement, the right-hand side is always evaluated fully before doing the actual setting of variables）:

x, y = y, x + y

等价于：

ham = y
spam = x + y
x = ham
y = spam

比如反转列表, 都不用考虑临时变量的存储，因为多重赋值语句自动帮我们存了：

def reverseList(self, head):
  cur, pre = head, None
  while cur:
    cur.next, prev, cur = pre, cur, cur.next
  return prev

此外以下赋值语句也关注一下：

a, a[0] = [1], 2  
# a == [2]