Python re.sub（）行首开始锚定

Question

考虑以下多行字符串：

>> print s
shall i compare thee to a summer's day?
thou art more lovely and more temperate
rough winds do shake the darling buds of may,
and summer's lease hath all too short a date.

re.sub()将所有and替换为AND：

>>> print re.sub("and", "AND", s)
shall i compare thee to a summer's day?
thou art more lovely AND more temperate
rough winds do shake the darling buds of may,
AND summer's lease hath all too short a date.

但是re.sub()不允许^锚定到该行的开头，因此添加它不会导致and被替换：

>>> print re.sub("^and", "AND", s)
shall i compare thee to a summer's day?
thou art more lovely and more temperate
rough winds do shake the darling buds of may,
and summer's lease hath all too short a date.

如何将re.sub()与行尾（^）或行尾（$）锚点结合使用？

Answer 1

您忘了启用多线模式。

re.sub("^and", "AND", s, flags=re.M)

  

re.M
  re.MULTILINE

     

指定时，模式字符'^'匹配字符串的开头和每行的开头（紧跟在每个换行符之后）;模式字符'$'在字符串的末尾和每行的末尾（紧接在每个换行符之前）匹配。默认情况下，'^'仅匹配字符串的开头，'$'仅匹配字符串的结尾，紧接在字符串末尾的换行符（如果有）之前。

source

flags参数不适用于早于2.7的python;所以在这些情况下你可以直接在正则表达式中设置它，如下所示：

re.sub("(?m)^and", "AND", s)

Answer 2

为多行添加(?m)：

print re.sub(r'(?m)^and', 'AND', s)

请参阅the re documentation here。