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POCorrectly parsing string literals with python's re module
 

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  1. POCorrectly parsing string literals with python's re module
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    <p>I'm trying to add some light markdown support for a javascript preprocessor which I'm writing in Python.</p> <p>For the most part it's working, but sometimes the regex I'm using is acting a little odd, and I think it's got something to do with raw-strings and escape sequences. </p> <p>The regex is: <code>(?&lt;!\\)\"[^\"]+\"</code></p> <p>Yes, I am aware that it only matches strings beginning with a <code>"</code> character. However, this project is born out of curiosity more than anything, so I can live with it for now. </p> <p>To break it down:</p> <pre><code>(?&lt;\\)\" # The group should begin with a quotation mark that is not escaped [^\"]+ # and match any number of at least one character that is not a quotation mark (this is the biggest problem, I know) \" # and end at the first quotation mark it finds </code></pre> <p>That being said, I (obviously) start hitting problems with things like this:</p> <p><code>"This is a string with an \"escaped quote\" inside it"</code></p> <p>I'm not really sure how to say "Everything but a quotation mark, unless that mark is escaped". I tried:</p> <pre><code>([^\"]|\\\")+ # a group of anything but a quote or an escaped quote </code></pre> <p>, but that lead to very strange results.</p> <p>I'm fully prepared to hear that I'm going about this all wrong. For the sake of simplicity, let's say that this regex will always start and end with double quotes (<code>"</code>) to avoid adding another element in the mix. I really want to understand what I have so far. </p> <p>Thanks for any assistance.</p> <p><strong>EDIT</strong></p> <p>As a test for the regex, I'm trying to find all string literals in the minified jQuery script with the following code (using the unutbu's pattern below):</p> <pre><code>STRLIT = r'''(?x) # verbose mode (?&lt;!\\) # not preceded by a backslash " # a literal double-quote .*? # non-greedy 1-or-more characters (?&lt;!\\) # not preceded by a backslash " # a literal double-quote ''' f = open("jquery.min.js","r") jq = f.read() f.close() literals = re.findall(STRLIT,jq) </code></pre> <p>The answer below fixes almost all issues. The ones that do arise are within jquery's own regular expressions, which is a very edge case. The solution no longer misidentifies valid javascript as markdown links, which was really the goal. </p>
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    1. USTom Thorogood
    1. USTom Thorogood
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    1. COIs there a reason you're trying to write your own Markdown parser instead of using one that's already debugged?
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    2. COBecause I want to learn.
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      1. USTom Thorogood
 

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