Flattening lists

Brian Allen Vanderburg II BrianVanderburg2 at aim.com
Thu Feb 5 17:10:51 CET 2009

mrkafk at gmail.com wrote:
> Baolong zhen wrote:
>> less list creation.
> At the cost of doing this at each 'flatten' call:
> if res is None:
>    res = []
> The number of situations of executing above code is the same as the 
> number of list creations (once for each 'flatten' call, obviously).
> Is list creation really more costly than above?
Probably not.  I wrote a small test program using a list several levels 
deep, each list containing 5 sublists at each level and finally just a 
list of numbers.  Flattening 1000 times took about 3.9 seconds for the 
one creating a list at each level, and 3.2 for the one not creating the 
list at each level.

Brian Vanderburg II

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