Specific iterator in one line

Rhodri James rhodri at wildebst.demon.co.uk
Tue Jun 30 11:26:33 CEST 2009


On Tue, 30 Jun 2009 09:44:39 +0100, Filip Gruszczyński  
<gruszczy at gmail.com> wrote:

> This is purely sport question. I don't really intend to use the answer
> in my code, but I am wondering, if such a feat could be done.
>
> I have a following problem: I have a list based upon which I would
> like to construct a different one. I could simply use list
> comprehensions, but there is an additional trick: for some elements on
> this list, I would like to return two objects. For example I have a
> list of 0s and 1s and for 0 I would like to add 1 'a' and for 1 I
> would like to add 2 'b', like this:
>
> [1, 0, 0, 1] -> ['b', 'b', 'a', 'a', 'b', 'b']
>
> The easy way is to return a tuple ('b', 'b') for 1s and then flatten
> them. But this doesn't seem very right - I'd prefer to create a nice
> iterable right away. Is it possible to achieve this? Curiosly, the
> other way round is pretty simple to achieve, because you can filter
> objects using if in list comprehension.
>
If you'll allow me a prior "import itertools",

>>> [i for e in [1,0,0,1] for i in itertools.repeat('ab'[e], e+1)]

does the job in 62 characters.

-- 
Rhodri James *-* Wildebeest Herder to the Masses



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