python 列表切片

只需要使用列表的一部分时，可以考虑创建切片，可指定要使用的第一个元素的索引和最后一个元素的索引加1，与函数range（）一样，python在到达你指定的第二个索引前面停止

提取列表的前3个元素

days = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"]
print(days[0:3])
// 输出结果为：
['Monday', 'Tuesday', 'Wednesday']

提取列表的2~4个元素

days = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"]
print(days[1:4])
//输出结果为：
['Tuesday', 'Wednesday', 'Thursday']

如果没有指定第一个元素，python将自动从列表开头开始

days = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"]
print(days[:4])
//输出结果为：
['Monday', 'Tuesday', 'Wednesday', 'Thursday']

如果没有指定最后一个元素，python将自动提取到结尾

days = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"]
print(days[1:])
//输出结果为：
['Tuesday', 'Wednesday', 'Thursday', 'Friday']

用负数索引提取元素，如提取最后三个元素

days = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"]
print(days[-3:])
//输出结果为：
['Wednesday', 'Thursday', 'Friday']

遍历切片

如果要遍历列表的部分元素，可在for循环中使用切片，如下：

days = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"]
for day in days[2:5]:
    print(day)
//输出结果为：
Wednesday
Thursday
Friday

复制列表

要复制列表，可创建一个包含整个列表切片，方法是同时省略第一个索引和最后索引，如下：

days = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"]
new_days = days[:]
print(new_days)
//输出结果为：
['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday']