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I'm not so able with regex and I'm looking for the syntax to exclude something.
I'm parsing <, >, " and & in html code (to replace with <, etc) and I need to exclude <br/> from parsing.
I.E.:
<html><br/>
<head><title></title></head><br/>
<body><br/>
</body><br/>
</html>
I tried sometihng like i.e.: r'<\b?![br]' and others, but they don't work completely. I use re.sub() to replace.
541
Ok, now the question is open again, I can do it as an answer, so...
Unless I'm missing something, and once it's just <br/> (not any variants), then can just replace <(?!br/>) with < and (?<!<br/)> with > and that's it?
In Python, it looks like that means this:
text = re.sub( '<(?!br/>)' , '<' , text )
text = re.sub( '(?<!<br/)>' , '>' , text )
To explain what's going on, (?!...) is a negative lookahead - it only successfully matches at a position if the following text does not match the sub-expression it contains.
(Note lookaheads do not consume the text matched by their sub-expression, they only verify if it exists, or not.)
Similarly, (?<!...) is a negative lookbehind, and does the same thing but using the preceding text.
However, lookbehinds do have a slight different to lookaheads (in some regex implementations) - which is that the sub-expressions inside lookbehinds must represent fixed-width or limited-width matches.
Python is one of the ones that requires a fixed width - so whilst the above expression works (because it's always four characters), if it was (?<!<br\s*/?)> then it would not be a valid regex for Python because it represents a variable length match. (However, you can stack multiple lookbehinds, so you could potentially manually iterate the assorted options, if that was necessary.)
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