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?highlight=list#list

首先Sequence type有三种

1. list
2. tuple
3. range

slice

[i:j:k]表示的是slice of s from i to j with step k, 对三种类型都有用

>>> 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: