详解Python3中的Sequence type的使用

其实本来是要reverse一下list的，就去查了一下list[::-1]是什么意思，发现还有很多要注意的地方，所以就记一下。
主要是参照https://docs.python.org/3/library/stdtypes.html"htmlcode">

> a = [1, 2, 3]
> a[::-1]
[3, 2, 1]
> a = (1, 2, 3)
> a[::-1]
(3, 2, 1)
> a = range(3)
> a[::-1]
range(2, -1, -1)

range中参数是range(start, stop[, step])
initialize a list

s * n表示的是n shallow copies of s concatenated
注意是浅拷贝哦，所以会有如下情况

> lists = [[]] * 3
> lists
[[], [], []]
> lists[0].append(3)
> lists
[[3], [3], [3]]

如果元素不是对象的话就没关系

> lists = [0] * 3
> lists
[0, 0, 0]
> lists[0] = 1
> lists
[1, 0, 0]

正确的初始化嵌套list的方法应该是

> lists = [[] for i in range(3)]
> lists[0].append(3)
> lists[1].append(5)
> lists[2].append(7)
> lists
[[3], [5], [7]]

concatenation pitfall

(感觉还是英文说的清楚些，这一点跟Java是一样的)
Concatenating immutable sequences always results in a new object. This means that building up a sequence by repeated concatenation will have a quadratic runtime cost in the total sequence length. To get a linear runtime cost, you must switch to one of the alternatives below: