Python using result of function for Regular Expression Substitution

Question

I have a block of text, and for every regex match, I want to substitute that match with the return value from another function. The argument to this function is of course the matched text.

I have been having trouble trying to come up with a one pass solution to this problem. It feels like it should be pretty simple.

Answer 1

Right from the documentation :

>>> def dashrepl(matchobj):
...     if matchobj.group(0) == '-': return ' '
...     else: return '-'
>>> re.sub('-{1,2}', dashrepl, 'pro----gram-files')
'pro--gram files'

Answer 2

Python-agnostic: Match everything before and everything after your text to replace.

/^(.*?)(your regexp to match)(.*)$/

Then you have the next before and after the text you're going to replace. The rest is easy -- just insert the result of your function between the two strings.