I'm not sure why it's useful to explode the stack with all that recursion? Mine didn't do that. The control flow is nearly identical, but it looks more fragile (and you would get some really evil stack trace if iter_factory(foo) happened to raise something other than TypeError).
It was a holdover from my first version which *was* recursive. When I switched to using your chaining style, I didn't think to get rid of the now unneeded recursion.
So just drop the recursive calls to 'walk', and it should be back to your structure.
For the 'infinite recursion on basestring' example, PJE at one point suggested a "if item is iterable" guard that immediately yielded the item. Allowing breadth first operation requires something a little different, though:
from itertools import chain
def walk(iterable, depth_first=True, atomic_types=(basestring,),
iter_factory=iter):
itr = iter(iterable)
while True:
for item in itr:
if isinstance(item, atomic_types):
yield item
continue
try:
subitr = iter_factory(item)
except TypeError:
yield item
continue
# Block simple cycles (like characters)
try:
subitem = subitr.next()
except StopIteration:
continue
if subitem is item:
yield subitem
continue
if depth_first:
itr = chain([subitem], subitr, itr)
else:
itr = chain(itr, [subitem], subitr)
break
else:
breakPy> seq [['123', '456'], 'abc', 'abc', 'abc', 'abc', ['xyz']] Py> list(walk(seq)) ['123', '456', 'abc', 'abc', 'abc', 'abc', 'xyz'] Py> list(walk(seq, depth_first=False)) ['abc', 'abc', 'abc', 'abc', '123', '456', 'xyz'] Py> list(walk(seq, atomic_types=())) ['1', '2', '3', '4', '5', '6', 'a', 'b', 'c', 'a', 'b', 'c', 'a', 'b', 'c', 'a', 'b', 'c', 'x', 'y', 'z'] Py> list(walk(seq, depth_first=False, atomic_types=())) ['a', 'b', 'c', 'a', 'b', 'c', 'a', 'b', 'c', 'a', 'b', 'c', '1', '2', '3', '4', '5', '6', 'x', 'y', 'z']
Raymond may simply decide to keep things simple instead, of course.
Cheers, Nick.
--
Nick Coghlan | [EMAIL PROTECTED] | Brisbane, Australia
---------------------------------------------------------------
http://boredomandlaziness.skystorm.net
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