gry@ll.mit.edu wrote:
> class Item(object):
> def __init__(self, value):
> self.val=value
> self.order = dict(c=0, a=1, d=2, b=3)
> def __cmp__(self, other):
> return cmp(self.order[self.val], self.order[other.val])
An object that keeps track of the order it's stored in an external container
seems bass-ackwards to me (if you'll pardon the expression). How do you
update the order? Why does every object need to carry around a global
ordering? What happens if you need two separate orderings like a,b,c,d and
a,c,d,b? And it isn't clear at all what the < operator is comparing in
your example:
a=Item('A')
b=Item('B')
if a < b: something
I'd put the ordering logic in the container instead. Something like this:
class mylist(list):
def before (me, a, b):
return me.index(a) < me.index(b)
l = mylist (['C', 'A', 'D', 'B'])
if l.before('A', 'D'):
something
This seems clearer and more flexible. You'll still have to handle
exceptions when a or b aren't in the list.
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