List Comprehension Question: One to Many Mapping?

[Boris Borcic]

Paul Rubin wrote:
> beginner <zyzhu2000 at gmail.com> writes:
>> For example, if I have x=[ [1,2], [3,4] ]
>>
>> What I want is a new list of list that has four sub-lists:
>>
>> [[1,2], [f(1), f(2)], [3,4], [f(3), f(4)]]
> 
> [[a, map(f,a)] for a in x]

no, that one will be [[[1,2], [f(1), f(2)]], [[3,4], [f(3), f(4)]]]
eg two sublists instead of four.

[map(g,a) for a in x for g in [None,f]]

will do it.

...a bit too cleverly, but there's worse :

list((yield a) or map(f,a) for a in x)

Cheers, BB