Specific iterator in one line

[Filip Gruszczyński]

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.

 

[Paul Rubin]

[1, 0, 0, 1] -> ['b', 'b', 'a', 'a', 'b', 'b']

Using itertools:

list(chain(*imap([['a'],['b','b']].__getitem__, [1,0,0,1])))

['b', 'b', 'a', 'a', 'b', 'b']

 

[Bearophile]

Filip Gruszczyñski:

[1, 0, 0, 1] -> ['b', 'b', 'a', 'a', 'b', 'b']

I like this version (43 golf holes), it's readable enough:

[c for d in[1,0,0,1]for c in("a","bb")[d]]

Bye,
bearophile