It does, although it also does the operation in place. I checked before writing it to be sure I wasn't misremembering.
>From the docs: These methods are called to implement the augmented arithmetic >assignments (+=, -=, *=, @=, /=, //=, %=, **=, <<=, >>=, &=, ^=, |=). These >methods should attempt to do the operation in-place (modifying self) and >return the result (which could be, but does not have to be, self)
