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开头：
示例：
"I went out on 1 sep 2012 and it was better than 15 jan 2012"
我想得到
"1 sep 2012, I went out on and it was better than 15 jan 2012"
我正在考虑替换"1 sep 2012"为",1 sep 2012,"，然后从中删除字符串，","但我不知道该写什么，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)
有什么帮助吗？
使用捕获组：
>>> import re
>>> s = "I went out on 1 sep 2012 and it was better than 15 jan 2012"
>>> r = re.compile('(^.*)(1 sep 2012 )(.*$)')
>>> r.sub(r'\2\1\3',s)
'1 sep 2012 I went out on and it was better than 15 jan 2012'
括号捕获部分字符串：
(^.*) # Capture everything from the start of the string
(1 sep 2012 ) # Upto the part we are interested in (captured)
(.*$) # Capture everything else
然后只需在替换`\2\1\3' 说明中重新排序捕获组：引用捕获组需要一个原始字符串r'\2\1\3'。我的示例中的第二组只是文字字符串(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（\s最后有一个额外的）：
(\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'
当存在 'r' 或 'R' 前缀时，反斜杠后面的字符将不加更改地包含在字符串中。