[canjobear]

Converting to a set in Python is extremely beneficial when you will be doing many `in` queries on the collection. But it isn't necessarily good in all cases, because converting the list to a set is itself O(n) and slower than `in`.

Example:

  In [1]: xs = range(10000)

  In [2]: %timeit 5000 in xs 
  100000 loops, best of 3: 77.8 µs per loop

  In [3]: %timeit 5000 in set(xs)
  1000 loops, best of 3: 235 µs per loop

  In [4]: xs_set = set(xs)

  In [5]: %timeit 5000 in xs_set
  10000000 loops, best of 3: 70.7 ns per loop