Yes, my notice is half valid. The is necessary for the actions, not for storing. Anyway, not a big difference in efficiency. :-) I mean, adding to set works with a builtin &quot;if&quot; that is slightly faster than an interpreted if line, and anyway, it will be executed.<br>
<br>        seenCategories.add(cat.title());<br>        if not cat.title() in seenCategories:<br>             # do something with this category<br>
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