selecting a random item from a set

[Jp Calderone]

On Wed, Dec 31, 2003 at 02:40:17AM +0000, Alexander Schmolck wrote:
> "Martin v. Loewis" <martin at v.loewis.de> writes:
> 
> > Alexander Schmolck wrote:
> > 
> > > Is there a better way? If not, how about something like Set.randompop()?
> > 
> > In principle, random.choice "ought to" work. 
> > It doesn't, as it expects the set to be indexable.
> 
> Maybe not insensibly -- the fairly generic approach outlined above that will
> work for any iterable with len is clearly not desirable as default (because of
> its time complexity), and just using it as a fallback won't work either,
> because AFACT there is no way for `choice` to find out whether its argument is
> a sequence or not.


    def choice(self, seq):
        """Choose a random element from a non-empty sequence."""
        try:
            return seq[int(self.random() * len(seq))]
        except TypeError:
            # Fallback algorithm

  Alternatively (not as nice, imho):

    def choice(self, seq):
        """Choose a random element from a non-empty sequence."""
        typeOrClass = getattr(seq, '__class__', type(seq))
        if hasattr(typeOrClass, '__getitem__'):
            return seq[int(self.random() * len(seq))]
        else:
            # Fallback algorithm

  Jp