python list comprehension to produce two values in one iteration

Use itertools.chain.from_iterable:

>>> from itertools import chain
>>> list(chain.from_iterable((i, i**2) for i in xrange(1, 6)))
[1, 1, 2, 4, 3, 9, 4, 16, 5, 25]

Or you can also use a generator function:

>>> def solve(n):
...     for i in xrange(1,n+1):
...         yield i
...         yield i**2

>>> list(solve(5))
[1, 1, 2, 4, 3, 9, 4, 16, 5, 25]