Hi, this is my first post, so go easy on me! :-)
I got this idea from the "cogen" discussion, seeing how the lack of a
reliable re-iterability test makes it hard to write lazy multi-pass
algorithms. Rather than (1) assuming iterators are re-iterable, (2)
"forcing" iterators to be re-iterable by eagerly converting them to
lists, or (3) trying to heuristically guess whether an iterator is
re-iterable, why not combine the best of (1) and (2) while avoiding (3)
entirely?
This class will lazily convert an interator to a list on the first pass
and then iterate over the saved list on all subsequent passes.
class reiter(object):
def __init__(self, iterable):
self.iterator = iter(iterable)
self.cache = []
def __iter__(self):
if self.iterator is None:
return iter(self.cache)
else:
return self
def next(self):
try:
element = self.iterator.next()
self.cache.append(element)
return element
except StopIteration:
self.iterator = None
raise
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