List、切片

一、List：是Python内置的数据类型列表--List，List是一种有序集合，可以随时删除和添加元素。

创建list直接用 []
1 letters = ["a","b","c","d","e"]
            0   1   2   3   4
print(letters[0])
a
print(letters[1])
b
#list中是通过索引来获取列表中的元素，索引是从0开始

如果说想要直接获取list的最后一个元素可以直接用-1的索引获取

>>> letters[-1]
'e'
>>> letters[-2]
'd'
>>> 

通过len()函数可以来获取列表中有多少个元素

>>> len(letters)
5
letters列表中有5个元素

List也是有相应的方法：

append()：在List最后一位添加元素

>>> letters.append("F")
>>> print(letters)
['a', 'b', 'c', 'd', 'e', 'F']

clear()：清空List

>>> letters = ["a","b","c","d","e",]
>>> letters.clear()
>>> print(letters)
[]

count(value)：在列表中该元素的个数

>>> letters = ["a","b","c","d","e","e","e"]
>>> letters.count("e")
3

extend()：扩展List，添加到该List的末尾

>>> letters = ["a","b","c","d","e"]
>>> numbers = [1,2,3,4,5]
>>> letters.extend(numbers)
>>> print(letters)
['a', 'b', 'c', 'd', 'e', 1, 2, 3, 4, 5]

index()：查找第一个出现的该元素在列表中的索引

>>> letters = ["a","b","c","d","e","e","e"]
>>> letters.index("e")
4

insert(index,p_object)：在List中添加元素

>> letters = ["a","b","c","d","e"]
>>> letters.insert(1,"A")
>>> print(letters)
['a', 'A', 'b', 'c', 'd', 'e']

pop(index = None)：通过索引删除病返回List中的元素，如果没有输入参数则默认删除List最后一个元素

>>> letters.pop()
'e'
>>> letters.pop(3)
'd'
>>> print(letters)
['a', 'b', 'c']

remove(value)：删除List中第一个出现的该元素

>>> letters = ["a","b","c","d","e","e","e"]
>>> letters.remove("e")
>>> print(letters)
['a', 'b', 'c', 'd', 'e', 'e']

reverse()：倒转List

>>> letters = ["a","b","c","d","e"]
>>> letters.reverse()
>>> print(letters)
['e', 'd', 'c', 'b', 'a']

sort()：将List中的元素从小到大排序

","f","d","a","e","5","e","e","2","$#aa"]
>>> letters.sort()
>>> print(letters)
['$#aa', '2', '5', '6', 'a', 'd', 'e', 'e', 'e', 'f']
>>> 

二、切片

关于切片，最初可能有些迷惑，但总结后思路就特别清晰：

[起始:结束:方向/间隔]

>>> letters = ["6","f","d","a","e","5","e","e","2","$#aa",2,4,2,4,5,66,7,33]
>>> letters[1:12:3] #表示从索引为1的元素开始取值，到索引12结束(不包括索引12的元素)，间隔为3
['f', 'e', 'e', 2]

[起始:结束:方向/间隔] 注意:如果想倒序切片，需要把"方向/间隔"改成负数

>>> letters = ["6","f","d","a","e","5","e","e","2","$#aa",2,4,2,4,5,66,7,33]
>>> letters[12:1:-3]
[2, '$#aa', 'e', 'a']