Why Is `{*l}` Faster Than `set(l)` - Python Sets (not Really Only For Sets, For All Sequences)

So here is my timings: >>> import timeit >>> timeit.timeit(lambda: set(l)) 0.7210583936611334 >>> timeit.timeit(lambda: {*l}) 0.5386332845236943 Why is

Solution 1:

For the same reason [] is faster than list(); the interpreter includes dedicated support for syntax based operations that uses specialized code paths, while constructor calls involve:

1. Loading the constructor from built-in scope (requires a pair of dict lookups, one in global scope, then another in built-in scope when it fails)
2. Requires dispatch through generic callable dispatch mechanisms, and generic argument parsing code, all of which is far more expensive than a single byte code that reads all of its arguments off the stack as a C array

All of these advantages relate to fixed overhead; the big-O of both approaches are the same, so {*range(10000)} won't be noticeably/reliably faster than set(range(10000)), because the actual construction work vastly outweighs the overhead of loading and calling the constructor via generic dispatch.