"Tom Anderson" <[EMAIL PROTECTED]> wrote:
> I'll just chip in and say i'd quite like a flatten(), too; at the moment,
> i have one like this:
>
> def flatten(ll):
> return reduce(lambda a, l: a.extend(l), ll, [])
This doesn't work; a.extend() returns None, not the extended list a:
>>> seq = [[1,2],[3],[],[4,[5,6]]]
>>> flatten(seq)
AttributeError: 'NoneType' object has no attribute 'extend'
This works for 1-level flattening:
def flatten(ll):
return reduce(lambda a, l: a.extend(l) or a, ll, [])
>>> flatten(seq)
[1, 2, 3, 4, [5, 6]]
And finally for recursive flattening:
def flatten(seq):
return reduce(_accum, seq, [])
def _accum(seq, x):
if isinstance(x,list):
seq.extend(flatten(x))
else:
seq.append(x)
return seq
>>> flatten(seq)
[1, 2, 3, 4, 5, 6]
George
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