Of these, only += on tuple elements and indexing with floats strike me as WTFs, and many others are evidence of the author really going out of their way to look for behaviors to nitpick on. The absolute majority of these are things that Python programmers either will never encounter, or can easily explain from Python &quot;first principles&quot; (e.g. most of the nitpicks on string and sequence behaviors).<p>I can tell you what I consider WTF worthy - things that I and others have undoubtedly been bitten by because they are ubiquitous. Those are mutable defaults, lack of loop scoping, and &quot;global&quot;&#x2F;&quot;nonlocal&quot; scoping. Oh, and add the crazy &quot;ascii&quot; I&#x2F;O encoding default on 2.7 (and the inability to cleanly reset it) to that list.