Python list v.s. set

Compared to append to list, add to set is about 70ns slower

• Cost of computing hash values, etc.
• This is a C-world cost, so it’s hard to shrink, even with PyPy or something like that.
  • As a result, as occurred in ABC176, “it is faster to make the loop spin than to make it unique with set. python

In [77]: timeit
    ...: xs = set()
    ...: xs.add(1)
    ...: 
141 ns ± 0.457 ns per loop (mean ± std. dev. of 7 runs, 10000000 loops each)

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