问个正则问题

[old9]

希望 match 到某几个特定单词的所有首次出现，比如下面这段文字（随便 copy 来的）：

Mr. Obama also used his own remarks to try to drive a wedge between Mr. Trump’ s campaign and Republican voters. “ It wasn ’ t particularly Republican and it sure wasn ’ t conservative,” he said of last week ’ s Republican convention. “ There were no serious solutions to pressing problems. Just the fanning of resentments and blame and hate and anger.” The president ’ s contempt for Mr. Trump took on a personal dimension as well when he recalled his grandparents from Kansas and said, “ I don ’ t know if they had their birth certificates ” — a reference to Mr. Trump’ s leadership of the so-called birther movement that raised questions about Mr. Obama’ s citizenship.

正则 (Obama|Trump) 会匹配到所有的 Obama 和 Trump （粗体的），现在希望仅匹配首次出现，即粗斜体的两个，研究了半天 lookbehind/back reference 啥的也没试出怎么写，求指导。

[old9]

用 lookahead 比如 (Obama|Trump)(?!.*\1) 可以匹配到最后出现的，我想着同理应该可以选到最开始出现的，但换成 lookbehind 发现 back reference 不能反着来，卡在这了……

[imn1]

用非贪婪模式就是第一个了，你用 findall 么？

[old9]

这里并没有 *、或 + 一类的标识，所以你是指 global flag ？但我需要的是前两个，不是第一个。
如果去掉 global ，则只能选中第一个 Obama ，没法选中第一个 Trump 。

[chairuosen]

JS 反正不支持 https://www.zhihu.com/question/20154937

[old9]

@chairuosen 噢原来这样，虽然我的环境不是 JS ，但也不是帖子里提到的有此功能的 .NET 。
那有没有什么方法可以绕过呢？不用 lookbehind 能实现么？

[arnofeng]

python 的 findall 然后列表的第一个

[chairuosen]

@old9 别用正则了呗。。。