"Christos" == TZOTZIOY <Christos> writes:
>> For quick-and-dirty stuff, it's often convenient to flatten a sequence
>> (which perl does, surprise surprise, by default):
>> >> [1,2,[3,"hello",[[4]]]] ->
>> >> [1, 2, 3, 'hello', 4]
Christos> See Python Library Reference, "5.16.3 Recipes". Now Christos> that all and any (also
The recipe is:
def flatten(listOfLists): return list(chain(*listOfLists))
That one is trivial, because it only flattens one level. The flattening I'm talking about involves flattening to arbitrary depth to get a single sequence of "atoms". The itertools implementation might also be able to avoid recursion by using a stack.
Here's a non-recursive implementation. There are lots around. One issue is specifying iterable types which should be atomic (notably strings). This uses a simple hardwired test for that.
def flatten(iterable):
stack = []
iterator = iter(iterable)
while 1:
try:
item = iterator.next()
if hasattr(item,"__iter__"): # Avoids iterating over strings
stack.append(iterator)
iterator = iter(item)
else:
yield item
except StopIteration:
if stack:
iterator = stack.pop()
else:
raise StopIteration>>> list(flatten([[[1,2,[3,[4,5]],[6,7,[8,[9],(10,11,12)]]]]])) [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12] >>> list(flatten(["abc","def",["ghi", "jkl"]])) ['abc', 'def', 'ghi', 'jkl']
Michael
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