On Thu, 07 Jul 2005 22:04:31 +0200, Thomas Heller <[EMAIL PROTECTED]> wrote:
>[EMAIL PROTECTED] (Bengt Richter) writes: > >> On Thu, 07 Jul 2005 09:51:42 +0200, Thomas Heller <[EMAIL PROTECTED]> wrote: >> >>>[EMAIL PROTECTED] (Bengt Richter) writes: >>> >>>> On Wed, 06 Jul 2005 17:57:42 +0200, Thomas Heller <[EMAIL PROTECTED]> >>>> wrote: >>>> >>>>>I'm trying to implement __iter__ on an abstract base class while I don't >>>>>know whether subclasses support that or not. >>> >>>> Will a property or custom descriptor do what you want? E.g. >>>> >>>> >>> class Base(object): >>>> ... def __getIter(self): >>>> ... if hasattr(self, "Iterator"): >>>> ... return self.Iterator >>>> ... raise AttributeError, name >>>> ... __iter__ = property(__getIter) >> [...] >>> >>>Yep, that's exactly what I need - thanks. >>> >> BTW, I forgot to mention that you could use property as a decorator >> in the above single-argument case: >> >> >>> class Base(object): >> ... @property >> ... def __iter__(self): >> ... if hasattr(self, "Iterator"): >> ... return self.Iterator >> ... raise AttributeError, name > >Of course. I didn't spot this, but I cannot use this anyway for 2.3 >compatibility. > >> ... >> >>> class Concrete(Base): >> ... def Iterator(self): >> ... yield 1 >> ... yield 2 >> ... yield 3 >> ... >> >>> iter(Base()) >> Traceback (most recent call last): >> File "<stdin>", line 1, in ? >> TypeError: iteration over non-sequence >> >>> iter(Concrete()) >> <generator object at 0x02EF152C> >> >>> list(iter(Concrete())) >> [1, 2, 3] >> >> Hope there isn't a gotcha for your use case in the way an instance attribute >> of the same name is allowed. A custom descriptor could eliminate that. >> >> >>> inst = Concrete() >> >>> list(iter(inst)) >> [1, 2, 3] >> >>> inst.__init__ = 'abc' >> >>> list(iter(inst)) >> [1, 2, 3] >> >>> inst.__init__ >> 'abc' > >I don't understand what you mean here. A __iter__ instance attribute? > Yes, but it seems very unlikely to cause a problem, especially since iter(inst) bypasses it, as you probably would want. In other words, never mind ;-) Regards, Bengt Richter -- http://mail.python.org/mailman/listinfo/python-list
