例如：
%20and%201=2%20union%20select%201,group_concat%28table_name%29,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20%20from%20information_schema.tables%20where%20table_schema=database%28%29
我想要截取指定字符串group_concat%28table_name%29前后的字符串，即 ：
%20and%201=2%20union%20select%201, 和 ,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20%20from%20information_schema.tables%20where%20table_schema=database%28%29
并分开保存他们，操作方法如下：
1 >>> s = '%20and%201=2%20union%20select%201,group_concat%28table_name%29,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20%20from%20information_schema.tables%20where%20table_schema=database%28%29'
2 >>> b = 'roup_concat%28table_name%29'
3 >>> before = s[:s.index(b)-1]
4 >>> after = s[s.index(b)+len(b):]
5 >>> before
6 '%20and%201=2%20union%20select%201,'
7 >>> after
8 ',3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20%20from%20information_schema.tables%20where%20table_schema=database%28%29'
9 >>>
灵活运用的话，可以截取你想要的任意字符段。