在 Python 中，如何提取以相同模式开头但没有不同结尾的多个文本块？

Question

给定一个测试字符串：

teststr= 'chapter 1 Here is a block of text from chapter one.  chapter 2 Here is another block of text from the second chapter.  chapter 3 Here is the third and final block of text.'

我想创建一个这样的结果列表：

result=['chapter 1 Here is a block of text from chapter one.','chapter 2 Here is another block of text from the second chapter.','chapter 3 Here is the third and final block of text.']

使用re.findall('chapter [0-9]',teststr)

我收到['chapter 1', 'chapter 2', 'chapter 3']

如果我想要的只是章节编号，那很好，但我想要章节编号加上直到下一个章节编号的所有文本。在最后一章的情况下，我想得到章号和一直到最后的文字。

尝试re.findall('chapter [0-9].*',teststr) 会产生贪婪的结果： ['chapter 1 Here is a block of text from chapter one. chapter 2 Here is another block of text from the second chapter. chapter 3 Here is the third and final block of text.']

我不擅长正则表达式，因此我们将不胜感激。

Answer 1

一般来说，提取正则表达式看起来像

(?s)pattern.*?(?=pattern|$)

或者，如果pattern 位于行首，

(?sm)^pattern.*?(?=\npattern|\Z)

在这里，你可以使用

re.findall(r'chapter [0-9].*?(?=chapter [0-9]|\Z)', text)

见this regex demo。 详情：

• chapter [0-9] - chapter + 空格和数字
• .*? - 任何零个或多个字符，尽可能少
• (?=chapter [0-9]|\Z) - 正向预测，匹配紧跟在 chapter、空格、数字或整个字符串结尾的位置。

这里，由于文本以关键字开头，您可以使用

import re
teststr= 'chapter 1 Here is a block of text from chapter one.  chapter 2 Here is another block of text from the second chapter.  chapter 3 Here is the third and final block of text.'
my_result = [x.strip() for x in re.split(r'(?!^)(?=chapter \d)', teststr)]
print( my_result )
# => ['chapter 1 Here is a block of text from chapter one.', 'chapter 2 Here is another block of text from the second chapter.', 'chapter 3 Here is the third and final block of text.']

请参阅Python demo。 (?!^)(?=chapter \d) 正则表达式的意思是：

• (?!^) - 找到一个不在字符串开头的位置并且
• (?=chapter \d) - 紧随其后的是 chapter、空格和任何数字。

该模式用于在找到的位置拆分字符串，并且不消耗任何字符，因此，在列表理解中，结果会从空格中删除。

Answer 2

如果您不必使用正则表达式，请尝试以下操作：

def split(text):
    chapters = []

    this_chapter = ""
    for i, c in enumerate(text):
        if text[i:].startswith("chapter ") and text[i+8].isdigit():
            if this_chapter.strip():
                chapters.append(this_chapter.strip())
            this_chapter = c
        else:
            this_chapter += c

    chapters.append(this_chapter.strip())

    return chapters

print(split('chapter 1 Here is a block of text from chapter one.  chapter 2 Here is another block of text from the second chapter.  chapter 3 Here is the third and final block of text.'))

输出：

['chapter 1 Here is a block of text from chapter one.', 'chapter 2 Here is another block of text from the second chapter.', 'chapter 3 Here is the third and final block of text.']

Answer 3

您正在寻找re.split。假设最多 99 章：

import re
teststr= 'chapter 1 Here is a block of text from chapter one.  chapter 2 Here is another block of text from the second chapter.  chapter 3 Here is the third and final block of text.'

chapters = [i.strip() for i in re.split('chapter \d{1,2}', teststr)[1:]]

输出：

['Here is a block of text from chapter one.',
 'Here is another block of text from the second chapter.',
 'Here is the third and final block of text.']