[$] Python dictionary "addition" and "subtraction"

A proposal to add a new dictionary operator for Python has spawned a PEPand two large threads on the python-ideas mailing list. To a certainextent, it is starting to look a bit like the "PEP 572 mess"; there are plenty of opinions onwhether the feature should be implemented and how it should be spelled, forexample. As yet, there has been no formal decision made on how the new steering council will be handling PEPpronouncements, though a reviewof open PEPs is the council's "highest priority". This PEP will presumably be added intothe process; it is likely too late to be included in Python 3.8 evenif it were accepted soon,so there is plenty of time to figure it all out before 3.9 is releasedsometime in 2021.