how to flatten one level of list of lists?

[Alex Martelli]

"George Young" <gry at ll.mit.edu> wrote in message
news:3B13DE0C.76270DAA at ll.mit.edu...
> I have a list like:
>   l = [[2], [3], [5], [11]]
> and I want to get:
>   ll = [2, 3, 5, 11]
>
> I know I can do something like:
>   ll = map(lambda i: i[0],l)
>
> but it seems like overkill to have to use a lamba for such a simple
> task.  Is there some easy way I'm missing?

List comprehension:
    ll = [x for y in l for x in y]
or
    ll = [x[0] for x in l]


> BTW, I tried to use l.__getitem__ or l.__getslice__ with map, but both
> failed with AttributeError.  (this is python 2.1)  The 2.1 docs seem to
> say these members exist for lists -- what's wrong?

Maybe ambiguous docs?  If you can pinpoint the erroneous parts,
they can no doubt be fixed...

You can use map if you wish, and without lambdas, but:

    import operator
    ll = map(operator.getitem, l, [0]*len(l))

...that's not very slick here imho, since you have to replicate the [0].
But even if you could bind l.getitem, how would it help you here?


Alex