使用正则表达式重新排序字符串

Question

我想将第一次出现的日期或一般的正则表达式带到我的文本的开头：

实施例： "I went out on 1 sep 2012 and it was better than 15 jan 2012" 而且我想得到 "1 sep 2012, I went out on and it was better than 15 jan 2012"

我在考虑用"1 sep 2012"替换",1 sep 2012,"，然后从","剪切字符串，但我不知道写什么而不是replace_with：

line = re.sub(r'\d+\s(?:jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\s\d{4}', 'replace_with', line, 1)

任何帮助？

Answer 1

使用capture groups：

>>> import re
>>> s = "I went out on 1 sep 2012 and it was better than 15 jan 2012"
>>> r = re.compile('(^.*)(1 sep 2012 )(.*$)')
>>> r.sub(r'\2\1\3',s)
'1 sep 2012 I went out on and it was better than 15 jan 2012'

Brackets捕获字符串的一部分：

(^.*)          # Capture everything from the start of the string
(1 sep 2012 )  # Upto the part we are interested in (captured)
(.*$)          # Capture everything else

然后只需对替换`\2\1\3' 注释中的捕获组重新排序：以引用捕获组，需要原始字符串r'\2\1\3'。我的示例中的第二个组只是文字字符串(1 sep 2012 )，但当然这可以是任何正则表达式，例如您创建的正则表达式（最后添加\s）：

(\d+\s(?:jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\s\d{4}\s)

>>> r = re.compile(r'(^.*)(\d+\s(?:aug|sep|oct|nov)\s\d{4}\s)(.*$)')
>>> r.sub(r'\2\1\3',s)
'1 sep 2012 I went out on and it was better than 15 jan 2012'

来自docs.python.org：

  

当存在'r'或'R'前缀时，字符串中包含反斜杠后面的字符不会发生变化。