Kelson Zawack <zawack...@gis.a-star.edu.sg> writes:
> Iterators however are a different beast, they are returned by the
> thing they are iterating over and thus any special cases can be
> covered by writing a specific implementation for the iterable in
> question. This sort of functionality is possible to implement,
> because java does it.
Note that you can wrap any iterator into a wrapper that implements
has_next along with the usual iteration protocol. For example:
class IterHasNext(object):
def __init__(self, it):
self.it = iter(it)
def __iter__(self):
return self
def next(self):
if hasattr(self, 'cached_next'):
val = self.cached_next
del self.cached_next
return val
return self.it.next()
def has_next(self):
if hasattr(self, 'cached_next'):
return True
try:
self.cached_next = self.it.next()
return True
except StopIteration:
return False
>>> it = IterHasNext([1, 2, 3])
>>> it.next()
1
>>> it.has_next()
True
>>> it.next()
2
>>> it.next()
3
>>> it.has_next()
False
>>> it.next()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 11, in next
StopIteration
--
http://mail.python.org/mailman/listinfo/python-list
