[Python-3000] Generic function PEP won't make it in time

Guido van Rossum guido at python.org
Wed Apr 25 02:01:10 CEST 2007

On 4/24/07, Bill Janssen <janssen at parc.com> wrote:
> Just to chime in...
> My preference would be to have "abstract" just mark classes that
> define an API, that define the "abstraction" of that particular
> interface.  Not carry over meanings from Java and C++ that "abstract"
> somehow always means "partial" or "incomplete".  I'd envision having
> "abstract" classes that are in fact also useful and complete
> implementations.  "Abstract" methods don't really make sense (to me)
> in Python.  This sounds very close to what Guido has already.
> Maybe "abstraction" is a better keyword than "abstract".
> Maybe it makes sense to have "abstraction" classes, and an
> "@ignorethismethod" decorator to mark methods that are *not* part of
> the abstraction, instead of "@abstractmethod" decorators to mark the
> methods that *are* part of the abstraction.

Hm, but sometimes characteristic methods are abstract, and in other
cases they are concrete. For exampe:

class Iterator(Iterable):
  def __next__(self):
    raise StopIteration
  def __iter__(self):  # This is abstract in Iterable, but concrete here
    return self

Both methods are part of the ABC. But only __next__ is abstract. Once
could define a perfectly valid empty iterator like this:

class EmptyIterator(Iterator):
  def __next__(self):
    return super(EmptyIterator, self).__next__()

--Guido van Rossum (home page: http://www.python.org/~guido/)

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