Question

In Python, you can get the numbers in a range by calling range(x,y). But given two ranges, say 5-15, and 10-20 how can you get all the numbers 5-20 without duplicates? The ranges may also be disjoint.

I could concat all the results and then uniquify the list, but is that the fastest solution?

Answer 1

>>> a = range(5, 15)
>>> b = range(10, 20)
>>> print sorted(set(a + b))
[5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]

Or if you want a more general expansion of the lists to their elements for inclusion in the set:

>>> list_of_lists = [a, b]
>>> print sorted(set(elem for l in list_of_lists for elem in l))
[5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]

And I found a way to compose it all in one line:

>>> list_of_lists = [a, b]
>>> print set.union(*map(set, list_of_lists))

Is sorting necessary? It’s just expository, but then I don’t see that sets necessarily output in sorted order:

>>> x = set(range(3))
>>> x
set([0, 1, 2])
>>> x.add(-1)
>>> x
set([0, 1, 2, -1])