Let me also add that even if it seems that my idea will not break any official contracts, I can create a new ABC class and let maps and sequence types inherit from it. IMHO it's absolutely not needed, but at least the discussion will be no more distracted my secondary considerations, since the main topic is about the usefulness and the advantage to have a base contract for maps and sequences.
PS: I intend to write: You've demonstrated to be a fair thinker, so do not fall into temptation to play with words. My English is terrible as much as StrangeDict code. -- https://mail.python.org/mailman/listinfo/python-list
