Question

I cannot find a way to serially search a string and append replacements. Let’s say I am implementing a templating language. A simplified template looks something like this:

Hello words on #DATE# in #COUNTRY# on this beautiful day.

Imagine a very long template, with many #SOMETHING# tags. Now I want to use regex to parse through this, and every time I found #SOMETHING#, do some python logic, replace it with some string, append it, and continue. All I found is that I can break the string up into tokens and matches and then reassemble it. Is there something better, without generating all those string chunks? Maybe I am trying to optimize too early, but in Java, we have the

appendReplacement(StringBuffer,String) and appendTail(StringBuffer)

methods and I was wondering if something similar can be done in Python.

See http://docs.oracle.com/javase/tutorial/essential/regex/matcher.html

Answer 1

You can use a function as the “replacement” in re.sub. Then re.sub will invoke your function for every match in the string, and the return value of the function will be the replacement in the string.