Question

I am trying to write a regex to match optionally quoted values (valid quotes are "' and `).
The rule is that the occurence of two quotes is an escaped quote.

Here is the regex I came up with:

(?P<quote>["'`])?(?P<value>(?(quote)((?!(?P=quote).)|((?=(?P=quote)).){2})*|[^\s;]*))(?(quote)(?P=quote)|)

And now in readable (with comments indicating what I think it does):

(?P<quote>["'`])?                   #named group Quote (any quoting character?)

    (?P<value>                      #name this group "value", what I am interested in
        (?(quote)               #if quoted 
            ((?!(?P=quote).)|((?=(?P=quote)).){2})* #see below
                                    #match either anything that is not the quote
                                    #or match 2 quotes
        |
            [^\s;]*         #match anything that is not whitespace or ; (my seperators if there are no quotes)
        )
    )

(?(quote)(?P=quote)|)               #if we had a leeding quote we need to consume a closing quote

It Performs fine for unquoted strings, quoted strings crash it with:

    match = re.match(regexValue, line)
  File "****/jython2.5.1/Lib/re.py", line 137, in match
    return _compile(pattern, flags).match(string)
RuntimeError: maximum recursion depth exceeded

what do I do wrong?

edit: Example input => output(for capturing group ‘value’ (desired)

text    => text
'text'  => text
te xt   => te
'te''xt'=> te''xt   #quote=' => strreplace("''","'") => desired result: te'xt
'te xt' => te xt

edit2: while looking at it i noticed a mistake, see below, however I believe the above to be still a valid re +> it might be a Jython bug, however it still does not do what I want it to do: (very subtle difference, point moved out of the lookahead group

new:(?P<quote>["'`])?(?P<value>(?(quote)((?!(?P=quote)).|((?=(?P=quote)).){2})*|[^\s;]*))(?(quote)(?P=quote)|)
old:(?P<quote>["'`])?(?P<value>(?(quote)((?!(?P=quote).)|((?=(?P=quote)).){2})*|[^\s;]*))(?(quote)(?P=quote)|)

Answer 1

I found the solution after a bit of fiddeling:

good:(?P<quote>["'`])?(?P<value>(?(quote)((?!(?P=quote)).|((?=(?P=quote)).){2})*|[^;\s]*))(?(quote)(?P=quote)|)
bad :(?P<quote>["'`])?(?P<value>(?(quote)((?!(?P=quote)).|((?=(?P=quote)).){2})*|[^\s;]*))(?(quote)(?P=quote)|)

and no I don’t understand the difference