Change a text between two strings in Python with Regex

python, regex

Solution

Use a combination of lookarounds in your regular expression.

reg = "(?<=%s).*?(?=%s)" % (str1,str2)

Explanation:

Lookarounds are zero-width assertions. They don't consume any characters on the string.

(?<=    # look behind to see if there is:
  gh    #   'gh'
)       # end of look-behind
.*?     # any character except \n (0 or more times)
(?=     # look ahead to see if there is:
  op    #   'op'
)       # end of look-ahead

Working Demo

Problem

I found several similar questions, but I cannot fit my problem to any of them. I try to find and replace a string between two other strings in a text. ``` reg = "%s(.*?)%s" % (str1,str2) r = re.compile(reg,re.DOTALL) result = r.sub(newstring, originaltext) ``` The problem is that the code above replace also `str1` and `str2`, whereas I want to replace only the text between them. Something obviously that I miss? Update: I simplified example: ``` text = 'abcdefghijklmnopqrstuvwxyz' str1 = 'gh' str2 = 'op' newstring = 'stackexchange' reg = "%s(.*?)%s" % (str1,str2) r = re.compile(reg,re.DOTALL) result = r.sub(newstring, text) print result ``` The result is `abcdefstackexchangeqrstuvwxyz` whereas I need `abcdefghstackexchangeopqrstuvwxyz`

Original source