Python, RegEx, Replace a certain part of a match

Question

I am trying to replace a certain part of a match that a regex found. The relevant strings have the following format:

"<Random text>[Text1;Text2;....;TextN]<Random text>"

So basically there can be N Texts seperated by a ";" inside the brackets. My goal is to change the ";" into a "," (but only for the strings which are in this format) so that I can keep the ";" as a seperator for a CSV file. So the result should be:

"<Random text>[Text1,Text2,...,TextN]<Random text>"

I can match the relevant strings with something like

re.compile(r'\[".*?((;).*?){1,4}"\]')

but if I try to use the sub method it replaces the whole string.

I have searched stackoverflow and I am pretty sure that "capture groups" might be the solution but I am not really getting there. Can anyone help me?

I ONLY want to change the ";" in the ["Text1;...;TextN"]-parts of my text file.

Answer 1

Try this regex:

;(?=(?:(?!\[).)*])

Replace each match with a ,

Click for Demo

Explanation:

• ; - matches a ;
• (?=(?:(?!\[).)*]) - makes sure that the above ; is followed by a closing ] somewhere later in the string but before any opening bracket [
  • (?=....) - positive lookahead
  • (?:(?!\[).)* - 0+ occurrences of any character which does not start with [
  • ] - matches a ]