The __sizeof__ special attribute shows up in dir(object) but appears not to be documented other than with

>>> help(object.__sizeof__)
Help on method_descriptor:
__sizeof__(...)
    __sizeof__() -> size of object in memory, in bytes

Should it have an entry in Lib 4.12. Special Attributes?

object.__sizeof__
    A method used by sys.getsizeof.

It should then show up in the index (missing now) and point people to sys.getsizeof.  Looking further, I see that it is mentioned but not indexed in the sys.getsizeof entry.