Need a strange sort method...

Ron Adam rrr at
Tue Oct 17 18:42:52 CEST 2006

Neil Cerutti wrote:
> On 2006-10-16, Tim Chase <python.list at> wrote:
>> If you need it in a flat list, rather than as a list of
>> chunk_size lists (which are handy for iterating over in many
>> cases), there are ways of obtaining it, such as the hackish
>>>>> sum([a[i::chunk_size] for i in range(chunk_size)], [])
>> [1, 4, 7, 10, 2, 5, 8, 3, 6, 9]
>> There are likely good recipes for flattening a list.  I just
>> happen not to have any at my fingertips.
> Actually, there isn't a good recipe in Python for flattening a
> list. They all come out tasting like Circus Peanuts (Turkish
> Delight for you non-Yanks).

Here's two that I came up with.  They are both very fast compared to anything 
else I've seen.  Maybe they won't taste so much like Peanuts.   :-)

def flatten(L):
     """ Flatten a list in place.
     i = 0
     while i < len(L):
         while type(L[i]) is list:
             L[i:i+1] = L[i]
         i += 1
     return L

def sflatten(sequence):
     """ Return a flattened sequence as a list.
     def iterinner(seq):
         for s in seq:
             if hasattr(s, '__iter__'):
                 for i in iterinner(s):
                     yield i
                 yield s
     return list(iterinner(sequence))

    Ron Adam

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