使用正則表達式重新排序字符串

Question

我想將第一次出現的日期或一般的正則表達式帶到我的文本的開頭：

例如： "I went out on 1 sep 2012 and it was better than 15 jan 2012" ，我希望得到"1 sep 2012, I went out on and it was better than 15 jan 2012"

我在想更換"1 sep 2012"與",1 sep 2012,"然后切割從字符串","但我不知道該怎么寫，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)

任何幫助？

Answer 1

使用捕獲組 ：

>>> 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'

括號捕獲字符串的一部分：

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

然后只需在替換`\\2\\1\\3' 注釋中重新排序捕獲組：要引用捕獲組，需要一個原始字符串r'\\2\\1\\3' 。 我的例子中的第二組只是文字字符串(1 sep 2012 )但當然這可以是任何正則表達式，例如你創建的那個（最后有一個額外的\\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'

來自docs.python.org ：

當存在'r'或'R'前綴時，字符串中包含反斜杠后面的字符而不進行更改。