[Python-ideas] Intermediate Summary: Fast sum() for non-numbers

[David Mertz]

On Sun, Jul 14, 2013 at 1:42 PM, David Mertz <mertz at gnosis.cx> wrote:

> Another approach in one of the links Sergey gave is nice too, and shorter
> and more elegant than any of his alternatives:
>
>   flat = []
>   map(flat.extend, list_of_lists)
>
> Using map() for a side effect is slightly wrong, but this is short,
> readable, and obvious in purpose.
>

Oh yeah.  That's a Python 2.x thing.  Now map() doesn't actually have
side-effects.  So you'd need to do:

  flat = []
  set(map(flat.extend, list_of_lists))

That starts to border on ugly.  One might also try:

  flat = []
  [flat.extend(l) for l in list_of_lists]

But I'm not thrilled by how that reads either.  Using the chain() versions
is just nicer.  Moreover, if you insist on concrete collections out of it,
you can take your pick (unlike sum().. although you can obviously wrap that
answer in a constructor too):

  flat_tup = tuple(chain(*iter_of_lists))
  flat_set = set(chain(list_of_lists))


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