Raymond Hettinger <rhettin...@users.sourceforge.net> added the comment:
FWIW, I'm happy with Guido's design of MutableMapping. It parallels all the other ABCs in its design and it succeeds completely at its primary role as a defining an interface. Its secondary role is to provide some mixin capability. It does well in this role when used as documented (just filling-in the abstract methods as letting the mixin do the rest). The case with OrderedDict is not a typical use of mixins because the primary class (dict) already provides all of methods demanded by the interface. I explicitly overwrite some of dict's methods because that is part of the behavior that OrderedDict wants to define differently than dict. It is appropriate that the primary class gets first dibs on defining a method and that intentional overrides are done explicitly (as they are in the OrderedDict example). With OrderedDict, the only reason we subclassed from dict was to provide interoperability with third-party tools that may have been hardwired to work only with dicts. In general, the preferred approach is to not subclass both dict and OrderedDict and to let the MutableMapping interface do its job. The proposed splitting of MutableMapping looks unhealthy and overly complex to me. It makes ABCs harder to use in the general case just to make one special case look a little prettier and do more of its magic implicitly. If this *really* bugs you, OrderedDict doesn't have to inherit from MutableMapping at all. We can throw code reuse out the window and just duplicate the relevant code fragments. To my eyes, either way is an explicit override of the dict's methods which is the intended effect. FWIW, the UserDict class in Py3.x was relocated to the collections module. It isn't gone. We made an effort to kill it but found that there were compelling use cases that were not a cleanly solved by any other approach. ---------- resolution: -> wont fix status: open -> closed _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue5402> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
