Python中两个重复关键字之间的子串获取方法

Question

表示字符串：

 string = 'Other unwanted text here and start here: This is the first sentence.\nIt is the second one.\nNow, this is the third one.\nThis is not I want.\n'

我想摘录前三句话

This is the first sentence.\nIt is the second one.\nNow, this is the third one.

显然，以下正则表达式不起作用：

re.search('(?<=This)(.*?)(?=\n)', string)

在This和第三个\n之间提取文本的正确表达式是什么？你知道吗

谢谢。你知道吗

Answer 1

(?s)(This.*?)(?=\nThis)

使.包含换行符为(?s)，查找以This开头，后跟\nThis的序列。你知道吗

别忘了，搜索结果的__repr__不会打印整个匹配的字符串，所以您需要

print(re.search('(?s)(This.*?)(?=\nThis)', string)[0])

Answer 2

Jerry是对的，regex不是合适的工具，有更简单更有效的方法来解决这个问题

this = 'This is the first sentence.\nIt is the second one.\nNow, this is the third one.\nThis is not I want.\n'

print('\n'.join(this.split('\n', 3)[:-1]))

输出：

This is the first sentence.

It is the second one.

Now, this is the third one.

如果您只是想练习使用regex，那么遵循教程会容易得多。你知道吗

Answer 3

您可以使用这个正则表达式捕获以This文本开头的三个句子

This(?:[^\n]*\n){3}

Demo

编辑：

Python代码

import re

s = 'Other unwanted text here and start here: This is the first sentence.\nIt is the second one.\nNow, this is the third one.\nThis is not I want.\n'

m = re.search(r'This(?:[^\n]*\n){3}',s)
if (m):
 print(m.group())

指纹

This is the first sentence.
It is the second one.
Now, this is the third one.