Setting it to None in the subclass is the intended pattern. But CPython must explicitly handle that somewhere so I don't know how general it is supported. Try defining a list subclass with __len__ set to None and see what happens. Then try the same with MutableSequence.
On Tue, Jun 7, 2016 at 10:37 AM, Ethan Furman <et...@stoneleaf.us> wrote: > For binary methods, such as __add__, either do not implement or return > NotImplemented if the other operand/class is not supported. > > For non-binary methods, simply do not define. > > Except for subclasses when the super-class defines __hash__ and the > subclass is not hashable -- then set __hash__ to None. > > Question: > > Are there any other methods that should be set to None to tell the > run-time that the method is not supported? Or is this a general mechanism > for subclasses to declare any method is unsupported? > > -- > ~Ethan~ > _______________________________________________ > Python-Dev mailing list > Python-Dev@python.org > https://mail.python.org/mailman/listinfo/python-dev > Unsubscribe: > https://mail.python.org/mailman/options/python-dev/guido%40python.org > -- --Guido van Rossum (python.org/~guido)
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