On Mon, 09 Aug 2010 09:11:37 -0700, daryn wrote:
> I'm just playing around with the iter function and I realize that I can
> use the iterator returned by it long after the original object has any
> name bound to it.
Yes, the same as everything else in Python. Iterators aren't unique here.
>>> a = [1,2,3]
>>> b = [None, a, None]
>>> id(a) == id(b[1]) # Same object, not a copy?
True
>>> del a
>>> print b
[None, [1, 2, 3], None]
> it seems as if the original object is never being garbage collected even
> though there is no name bound to it.
Of course not. That would be a Bad Thing if Python garbage collected an
object while other objects were still using it. Can you say "core dump"?
> Does the name bound to the
> iterator object count as a reference to the original object for garbage
> collection purposes?
No, but the iterator itself does.
The technique is called *reference* counting, not "name counting". Each
name is a reference, but not every reference is a name.
> Is there some way to retrieve/manipulate the
> original object via the iterator?
Depends on the iterator. For the standard iterator created by iter(), I
don't think so. But for a custom iterator type, there can be if you want:
class MyIter(object):
"""Quick and dirty iterator."""
def __init__(self, data):
self.data = data
self.i = 0
def __iter__(self):
return self
def next(self):
try:
o = self.data[self.i]
except IndexError:
raise StopIteration
self.i += 1
return o
>>> it = MyIter([1,2,3,4])
>>> it.next()
1
>>> del it.data[1:3]
>>> it.next()
4
--
Steven
--
http://mail.python.org/mailman/listinfo/python-list
