WTFPython: Exploring and understanding Python through surprising snippets

I have a mildly surprising snippet which I believe they don't have. It's about interaction of class and instance attributes with behavior of "X += Y". Python expands it to "X = X + Y" but only if X implements "+" but not "+=" class A: a = (1,) # tuples are immutable and don't have "+=" b = [1,] # lists have "+=" obj = A() obj.a += (2,) # this creates obj.a obj.b += (2,) # this modifies…

I feel like WTFs caused by doing something deeply weird hardly counts against the language. Yes doing the walrus operator inside brackets works. Yes of course it's going to be doing weird things. Is this really surprising to anyone? It's not what that operator is for. Yes comparing strings with "is" works sometimes. It's not checking equality and it isn't supposed to. In another implementation using "is" might work all the time or none of the time. Don't use "is"…

Auch. Quite a few of these stem from the design mistake to allow cross-type equality tests combined with a hard headed effort to try to make it work. >>> 2 == 2L True >>> hex(2) == hex(2L) False >>> type(2) <type 'int'> >>> type(2L) <type 'long'> >>>

There are some good ones in there! I especially like that explanations are given and the optimizations that CPython makes are revealed.