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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?
974
The \[[^\]]*]\[ matches [ , then any 0+ chars other than ] and then ][ . The (...) forms a capturing group #1, it will remember the value that you will be able to get into the replacement with $1 backreference. [^\]]* matches 0+ chars other than ] and this will be replaced.
If you want to replace a string that matches a regular expression (regex) instead of perfect match, use the sub() of the re module. In re. sub() , specify a regex pattern in the first argument, a new string in the second, and a string to be processed in the third.
By default, the count is set to zero, which means the re. sub() method will replace all pattern occurrences in the target string.
Python String | replace() replace() is an inbuilt function in the Python programming language that returns a copy of the string where all occurrences of a substring are replaced with another substring.
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)?\.([^\.]*)$' , r'_suff.\2',"long.file.name.jpg") 
re.sub(r'(?:_a)?\.([^.]*)$', 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 _a
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
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