Armin Ronacher wrote:
Greg Ewing <greg.ewing <at> canterbury.ac.nz> writes:
Well, I'm skeptical about the whole ABC thing in the
first place -- it all seems very unpythonic to me.
I think it's very pythonic and the very best solution to interfaces *and*
duck typing. Not only does it extend duck-typing in a very, very cool way
but also does it provide a very cool way to get custom sets or lists going
with few extra work. Subclassing builtins was always very painful in the
past and many used the User* objects which however often broke because some
code did something like isinstance(x, (tuple, list)). Of course one could
argue that instance checking is the root of all evil but there are
situations where you have to do instance checking. And ABCs are the
perfect solution for that as they combine duck-typing and instance
checking.
In my oppinion ABCs are the best feature of 2.6 and 3.0.
But another way of thinking about it is that we
already have an ABC of sorts for strings, and it's
called basestring. It might be better to enhance
that with whatever's considered missing than
introducing another one.
basestring is not subclassable for example. Also it requires subclassing
which ABCs do not.
I would be strongly +1 on a string ABC. Currently (to my knowledge)
there is no way of using duck typing for built-in APIs that expect a
string. How do I pass in an object to 'open' for example that isn't
actually a string or subclass?
>>> class X(object):
... def __unicode__(self):
... return 'fish'
... __str__ = __repr__ = __unicode__
...
>>> x = X()
>>> open(x)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: coercing to Unicode: need string or buffer, X found
>>> unicode(x)
u'fish'
Michael Foord
Regards,
Armin
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