None, True, False are singletons and are never constructed again after initilization of the interpreter (and have been keywords in python2). That's why "is" is always safe.

Small integers, as they are kept around, probably are as well (5 is (2+3) works).

I think what gets dropped during the conversation is, that we've been living with Java doing it this way (is being == and == being .equals) for decades and nobody really complains.