In [22]: x=range(0,10000)

In [23]: y=range(10000,20000)

In [24]: %timeit x+y
1000 loops, best of 3: 242 µs per loop

In [25]: %timeit set(x+y)
1000 loops, best of 3: 1.43 ms per loop

In [26]: %timeit list(set(x+y))
1000 loops, best of 3: 1.81 ms per loop