On Feb 22, 2006, at 7:21 AM, Raymond Hettinger wrote:
...
> I'm somewhat happy with the patch as it stands now. The only part
> that needs serious rethinking is putting on_missing() in regular
> dicts. See my other email on that subject.
What if we named it _on_missing? Hook methods intended only to be
overridden in subclasses are sometimes spelled that way, and it
removes the need to teach about it to beginners -- it looks private
so we don't explain it at that point.
My favorite example is Queue.Queue: I teach it (and in fact
evangelize for it as the one sane way to do threading;-) in "Python
101", *without* ever mentioning _get, _put etc -- THOSE I teach in
"Patterns with Python" as the very bext example of the Gof4's classic
"Template Method" design pattern. If dict had _on_missing I'd have
another wonderful example to teach from! (I believe the Library
Reference avoids teaching about _get, _put etc, too, though I haven't
checked it for a while).
TM is my favorite DP, so I'm biased in favor of Guido's design, and I
think that by giving the hook method (not meant to be called, only
overridden) a "private name" we're meeting enough of your and /F's
concerns to let _on_missing remain. Its existence does simplify the
implementation of defaultdict (and some other dict subclasses), and
"if the implementation is easy to explain, it may be a good idea",
after all;-)
Alex
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