python3.10.0字符串基础

字符串支持 索引 （下标访问），第一个字符的索引是 0。单字符没有专用的类型，就是长度为一的字符串：

1. >>> word = 'Python'
2. >>> word[0] # character in position 0
3. 'P'
4. >>> word[5] # character in position 5
5. 'n'

索引还支持负数，用负数索引时，从右边开始计数：

1. >>> word[-1] # last character
2. 'n'
3. >>> word[-2] # second-last character
4. 'o'
5. >>> word[-6]
6. 'P'

注意，-0 和 0 一样，因此，负数索引从 -1 开始。

除了索引，字符串还支持 切片。索引可以提取单个字符，切片 则提取子字符串：

1. >>> word[0:2] # characters from position 0 (included) to 2 (excluded)
2. 'Py'
3. >>> word[2:5] # characters from position 2 (included) to 5 (excluded)
4. 'tho'
5. 切片索引的默认值很有用；省略开始索引时，默认值为 0，省略结束索引时，默认为到字符串的结尾：
   1. >>> word[:2] # character from the beginning to position 2 (excluded)
   2. 'Py'
   3. >>> word[4:] # characters from position 4 (included) to the end
   4. 'on'
   5. >>> word[-2:] # characters from the second-last (included) to the end
   6. 'on'