On Fri, 23 Oct 2009 05:39:53 am Brett Cannon wrote: > > Is __doc__ not normal due to its general underscorishness, or is it > > not normal because it isn't? > > I honestly don't follow that sentence. But __doc__ is special because > of its use; documenting how to use of an object. In this case when > you call something like help() on an instance of an object it skips > the instance's value for __doc__ and goes straight to the defining > class and stops there as you don't care how a subclass says to use > itself as that is not what you are working with. Classes don't normally inherit behaviour from their subclasses. Presumably you meant superclass. I expected __doc__ to be just like the other double-underscore objects: lookup skips the instance and goes to the class, then follows the normal rules of inheritance. Consequently I've just discovered that a few of my classes, which I assumed inherited __doc__, don't actually have a docstring. This has consequences beyond help(obj) not working as expected: doctests which I thought were running aren't. Magic behaviour like this is nasty because it breaks the Rule of Least Astonishment. I thought I understood Python's object model and it's rules of inheritance, but not only do double-underscore attributes follow a different rule for inheritance than other attributes, but __doc__ follows a different rule than other double-underscore attributes. -- Steven D'Aprano
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