list comprehension for splitting strings into pairs

[Steven Bethard]

Russell Blau <russblau <at> hotmail.com> writes:

> >>> lst = ['1', '1:2', '3', '-1:4']
> >>> splits = [':' in item and item.split(':', 1) or [item, None]
>               for item in lst]
> >>> splits
> [['1', None], ['1', '2'], ['3', None], ['-1', '4']]

Oooh.  Pretty.  =)

What if I want to convert my splits list to:

[[1, None], [1, 2], [3, None], [-1, 4]]

where I actually call int on each of the non-None items?  Obviously I could 
extend your example to:

>>> lst = ['1', '1:2', '3', '-1:4']
>>> splits = [':' in item and [int(x) for x in item.split(':', 1)]
...           or [int(item), None]
...           for item in lst]
>>> splits
[[1, None], [1, 2], [3, None], [-1, 4]]

But that's getting to be a bit more work than looks good to me in a list 
comprehension.  I thought about doing it in two steps:

>>> splits = [':' in item and item.split(':', 1) or [item, None]
...           for item in lst]
>>> splits = [[int(i), p is not None and int(p) or p]
...           for i, p in splits]
>>> splits
[[1, None], [1, 2], [3, None], [-1, 4]]

This looks decent to me, but if you see a better way, I'd love to hear about 
it. =)

Thanks again!

Steve