Flattening lists

Mensanator mensanator at aol.com
Sat Feb 7 00:55:14 CET 2009


On Feb 6, 3:23 pm, Rhamphoryncus <rha... at gmail.com> wrote:
> On Feb 5, 1:16 pm, Michele Simionato <michele.simion... at gmail.com>
> wrote:
>
> > On Feb 5, 7:24 pm, a... at pythoncraft.com (Aahz) wrote:
>
> > > In article <a22c77c4-a812-4e42-8972-6f3eedf72... at l33g2000pri.googlegroups.com>,
> > > Michele Simionato  <michele.simion... at gmail.com> wrote:
>
> > > >Looks fine to me. In some situations you may also use hasattr(el,
> > > >'__iter__') instead of isinstance(el, list) (it depends if you want to
> > > >flatten generic iterables or only lists).
>
> > > Of course, once you do that, you need to special-case strings...
>
> > Strings are iterable but have no __iter__ method, which is fine in
> > this context, since I would say 99.9% of times one wants to treat them
> > as atomic objects, so no need to special case.
>
> Don't worry, that little oddity was fixed for you:
>
> Python 3.0+ (unknown, Dec  8 2008, 14:26:15)
> [GCC 4.3.2] on linux2
> Type "help", "copyright", "credits" or "license" for more information.>>> str.__iter__
>
> <slot wrapper '__iter__' of 'str' objects>>>> bytes.__iter__
>
> <slot wrapper '__iter__' of 'bytes' objects>>>> bytearray.__iter__
>
> <slot wrapper '__iter__' of 'bytearray' objects>
>
> I'm in the "why do you need more than 1 depth?" camp.  Dispatching
> based on your own type should be given an extra look.  Dispatching
> based passed in types should be given three extra looks.
>
> I didn't realize itertools.chain(*iterable) worked.  I guess that
> needs to be pushed as the canonical form.

What about this (from the Recipes section of the itertools manual)?

def flatten(listOfLists):
    return list(chain.from_iterable(listOfLists))



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