Pythonic way to create union of all values contained in multiple lists

set.union does what you want:

>>> results_list = [[1,2,3], [1,2,4]]
>>> results_union = set().union(*results_list)
>>> print(results_union)
set([1, 2, 3, 4])

You can also do this with more than two lists.

Since you seem to be using Python 2.5 (it would be nice to mention in your Q if you need an A for versions != 2.6, the current production one, by the way;-) and want a list rather than a set as the result, I recommend:

import itertools

...

return list(set(itertools.chain(*result_list)))

itertools is generally a great way to work with iterators (and so with many kinds of sequences or collections) and I heartily recommend you become familiar with it. itertools.chain, in particular, is documented here.

in comprehension way:

[*{ j for i in lists for j in i }]

or

[*functools.reduce(lambda x,y: {*x, *y}, lists)]

Unions are not supported by lists, which are ordered, but are supported by sets. Check out set.union.

I used the following to do intersections, which avoids the need for sets.

a, b= [[1,2,3], [1,2]]
s = filter( lambda x: x in b, a)

or,

s = [ x for x in b if x in a ]

desired_result = [x for y in lists for x in y]