[issue9523] Improve dbm modules

[Éric Araujo]

Éric Araujo <merwok at netwok.org> added the comment:

> Here is my updated patch:
You don’t have to attach a file here, just update the codereview page instead.  Or maybe you can’t because I created the page?

> 1, Now the dbm view objects are the same as dict view objects, which
> are in conformity with collections.KeysView, ValuesView and ItemsView.
Great!  Just to make sure: How do you know that the view objects are compliant?  Do you test all the methods documented for the ABCs?

> 2, I register all these abcs explicitly because these abcs have not
> __subclasshook__() method so they can't check api conformance(at
> lease exist) through isinstance(). I could not make sure api
> conformance except testing each method I find in abc explicitly. And
> my test_abc() is just to test the registering.

Thank you for repeating that many times and politely: I was indeed wrong.  I went back to  PEP 3119 to read again about __instancecheck__ and __subclasscheck__, then experimented in a shell and was surprised.  I have been misunderstanding one thing: issubclass(cls, abc) does not return true automatically if cls provides the methods, it’s entirely up to the ABC to check methods or do something else in its __subclasscheck__ or __instancecheck__ methods.  (I should have known better, I was in a discussion about adding that very feature on python-ideas and #9731!)  After another bit of experimentation with dict views and collections ABCs, I finally understand that you have to register your view classes.  Thanks for letting me correct my misunderstanding.

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue9523>
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