I need to match two cases by one reg expression and do replacement
'long.file.name.jpg' -> 'long.file.name_suff.jpg'
'long.file.name_a.jpg' -> 'long.file.name_suff.jpg'
I'm trying to do the following
re.sub('(\_a)?\.[^\.]*$' , '_suff.',"long.file.name.jpg")
But this is cut the extension '.jpg' and I'm getting
long.file.name_suff. instead of long.file.name_suff.jpg I understand that this is because of [^.]*$ part, but I can't exclude it, because I have to find last occurance of '_a' to replace or last '.'
Is there a way to replace only part of the match?
re.sub(r'(?:_a)?\.([^.]*)$', r'_suff.\1', "long.file.name.jpg")
?: starts a non matching group (SO answer), so
(?:_a) is matching the
_a but not enumerating it, the following question mark makes it optional.
So in English, this says, match the ending
.<anything> that follows (or doesn't) the pattern
Another way to do this would be to use a lookbehind (see here). Mentioning this because they're super useful, but I didn't know of them for 15 years of doing REs
Put a capture group around the part that you want to preserve, and then include a reference to that capture group within your replacement text.
re.sub(r'(\_a)?\.([^\.]*)$' , r'_suff.\2',"long.file.name.jpg")