What is the fastest way to get the first key in a dictionary?

fastest_first_key.py

from time import perf_counter_ns

NANOS_PER_SECOND = 1_000_000_000

ITER_COUNT = 100_000

biased_dict = {"one_key_to_rule_them_all": 42}


def first_1():
    return next(iter(biased_dict))


def first_2():
    return list(biased_dict)[0]


def first_3():
    return next(iter(biased_dict.keys()))


def first_4():
    return list(biased_dict.keys())[0]


def first_5():
    for key in biased_dict:
        return key


def first_6():
    for key in biased_dict.keys():
        return key


def first_7():
    for key, v in biased_dict.items():
        return key


def benchmark(fn):
    start_ns = perf_counter_ns()
    for _ in range(ITER_COUNT):
        fn()
    end_ns = perf_counter_ns()
    duration_ns = end_ns - start_ns
    return {
        "duration_ns": duration_ns,
        "ns_per_iteration": duration_ns / ITER_COUNT,
        "iterations_per_sec": int(NANOS_PER_SECOND // (duration_ns / ITER_COUNT)),
    }


def main():
    results = {}
    for fn_name, fn in [
        ("first_1", first_1),
        ("first_2", first_2),
        ("first_3", first_3),
        ("first_4", first_4),
        ("first_5", first_5),
        ("first_6", first_6),
        ("first_7", first_7),
    ]:
        benchmark(fn)
        results[fn_name] = benchmark(fn)
    sorted_results = sorted(results.items(), key=lambda item: item[1]["duration_ns"])
    print("Results are printed with the fastest function at the top, and the slowest at the bottom")
    fastest_fn_name, fastest_result = sorted_results[0]
    slowest_fn_name, slowest_result = sorted_results[-1]
    for fn_name, result in sorted_results:
        if fn_name == fastest_fn_name:
            print(fn_name + " (Fastest!):")
        else:
            x_slower_than_fastest = result["duration_ns"] / fastest_result["duration_ns"]
            print(f"{fn_name} ({x_slower_than_fastest:.2}x slower than {fastest_fn_name}):")

        print(f"    duration: {result['duration_ns']}ns")
        print(f"    ns_per_iteration: {result['ns_per_iteration']}ns")
        print(f"    iterations_per_sec: {result['iterations_per_sec']} per second")


if __name__ == "__main__":
    main()