[Tutor] Regex

[Andrei]

I'm quite sure I've seen a question of this type before, but I seem 
unable to find it. How can I match a re pattern ONLY if it is not 
preceded by another re pattern? I know how to construct both individual 
regexes, but I don't know how to glue them together in order to achieve 
this.

Think for example of finding all URLs in a piece of text, but *not* if 
they are inside link tags and therefore preceded by 'href="'.
<a href="http://python.org">Python</a> shouldn't give a match, but 
http://python.org on its own should.

Andrei

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