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POHow can I substitute an expression {{ text }} with re.sub() when 'text' may include further {{ text }} blocks?
 

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  1. POHow can I substitute an expression {{ text }} with re.sub() when 'text' may include further {{ text }} blocks?
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    <p>I'm trying to parse raw wikipedia article content, e.g. <a href="http://en.wikipedia.org/w/index.php?title=Sweden&amp;action=raw" rel="nofollow">the article on Sweden</a>, using <code>re.sub()</code>. However, I am running into problems trying to substitute blocks of <code>{{some text}}</code>, because they can contain further blocks of <code>{{some text}}</code>.</p> <p>Here's an abbreviated example from the above article:</p> <pre><code>{{Infobox country | conventional_long_name = Kingdom of Sweden | native_name = {{native name|sv|Konungariket Sverige|icon=no}} | common_name = Sweden }} Some text I do not want parsed. {{Link GA|eo}} </code></pre> <p>The curly braces within curly braces recursion could theoretically be arbitrarily nested to any number of levels.</p> <p>If I match the greedy block of <code>{{.+}}</code>, everything is matched from <code>{{Infobox</code> to <code>eo}}</code>, including the text I do not want matched.</p> <p>If I match the ungreedy block of <code>{{.+}}</code>, the part from <code>{{Infobox</code> to <code>icon=no}}</code> is matched, as is <code>{{Link GA|eo}}</code>. But then I'm left with the string <code>| common_name [...] not want parsed.</code></p> <p>I also tried variants of <code>\{\{.+(\{\{.+\}\})*.+\}\}</code> and <code>\{\{[^\{]+(\{\{[^\{]+\}\})*[^\{]+\}\}</code>, in the hopes of matching only sub-blocks within the larger block, but to no avail.</p> <p>I'd list all of what I've tried, but I honestly can't remember half and I doubt it'd be of much use anyway. It always comes back to the same problem: that for the double curly end braces <code>}}</code> to match, there needs to have been the same number of <code>{{</code> occurrences beforehand.</p> <p>Is this even solvable using regular expressions, or do I need another solution?</p>
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    1. USJoel Hinz
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      1. POHow can I substitute an expression {{ text }} with re.sub() when 'text' may include further {{ text }} blocks?
      1. USthefourtheye
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      1. POHow can I substitute an expression {{ text }} with re.sub() when 'text' may include further {{ text }} blocks?
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    1. COWhen there are nested patterns, grammars are the way to go.
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      1. POHow can I substitute an expression {{ text }} with re.sub() when 'text' may include further {{ text }} blocks?
      1. USthefourtheye
    2. COOf possible interest: [Python MediaWiki parser](https://github.com/pediapress/mwlib), which apparently wikipedia itself uses (for pdf export)
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      1. POHow can I substitute an expression {{ text }} with re.sub() when 'text' may include further {{ text }} blocks?
      1. USDanielB
    3. CO"Is this even solvable using regular expressions" -- [not with standard regexes, no](http://stackoverflow.com/questions/133601/can-regular-expressions-be-used-to-match-nested-patterns). Paired delimiters and recursion are exactly where they fall down. However, most regex libraries can actually handle this because of lookahead and lookbehind extensions.
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      1. POHow can I substitute an expression {{ text }} with re.sub() when 'text' may include further {{ text }} blocks?
      1. USJosh Caswell
 

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