Performance comparsion between long if-else and mapped function

code.py

def fn_ifelse(i):
    if i == 0:
        return i
    elif i == 1:
        return i
    elif i == 2:
        return i
    elif i == 3:
        return i
    elif i == 4:
        return i
    elif i == 5:
        return i
    elif i == 6:
        return i
    else:
        return i
def fn_table_build():
    def sub_0(i):
        return i
    def sub_1(i):
        return i
    def sub_2(i):
        return i
    def sub_3(i):
        return i
    def sub_4(i):
        return i
    def sub_5(i):
        return i
    def sub_6(i):
        return i
    def sub_7(i):
        return i
    table = {
        0: sub_0,
        1: sub_1,
        2: sub_2,
        3: sub_3,
        4: sub_4,
        5: sub_5,
        6: sub_6,
    }
    def fn_main(i):
        return table.get(i, sub_7)(i)
    return fn_main
fn_table = fn_table_build()

ifelse-vs-function-dict.py

"""
Roughly 12 branches can beat mapped function
"""
from __future__ import annotations

import itertools
from timeit import timeit
from typing import List


def func_body(i):
    # all are identity function
    return "return i"


def fn_source(name, args, body: List[str]):
    lines = ['def %s(%s):' % (name, ','.join(args))]
    lines.extend([f"    {s}" for s in body])
    return '\n'.join(lines)


def ifelse_setup_code(n):
    assert n >= 2

    body = []

    for i in range(n):
        if i == 0:
            cond = f"if i == {i}:"
        elif i == n - 1:
            cond = f"else:"
        else:
            cond = f"elif i == {i}:"

        body.extend((
            cond,
            f'    {func_body(i)}',
        ))

    return fn_source('fn_ifelse', ('i',), body)


def map_setup_code(n):
    assert n >= 2

    def create_subfn(id_):
        return fn_source(f'sub_{id_}', ('i',), [func_body(id_)])

    lines = []
    for i in range(n):
        lines.extend(create_subfn(i).split('\n'))
    lines.append('table = {')

    for i in range(n - 1):
        lines.append(f'    {i}: sub_{i},')
    lines.append('}')
    main_body = []
    main_body.append(f'return table.get(i, sub_{n - 1})(i)')
    #
    # main_body.extend((
    #     'try:',
    #     '    return table[i](i)',
    #     'except KeyError:',
    #     f'    return sub_{n - 1}(i)',
    # ))

    lines.extend(fn_source('fn_main', ('i',), main_body).split('\n'))
    lines.append('return fn_main')

    s = fn_source('fn_table_build', (), lines)
    return '\n'.join(itertools.chain(s.split('\n'), [
        'fn_table = fn_table_build()',
    ]))


def main():
    for n in range(10, 32):
        source = '\n'.join((ifelse_setup_code(n), map_setup_code(n)))
        ns = {}
        exec(source, None, ns)

        fn_ifelse = ns['fn_ifelse']
        fn_table = ns['fn_table']
        assert fn_ifelse(n // 2) == n // 2, n
        assert fn_table(n // 2) == n // 2, n
        number = 1_000_000
        print('n', n)
        # print(source)
        print('ifelse', timeit('[fn(i) for i in range(n)]', 'fn = fn_ifelse', globals=locals(), number=number) / n)
        print('table', timeit('[fn(i) for i in range(n)]', 'fn = fn_table', globals=locals(), number=number) / n)
        print()


if __name__ == '__main__':
    main()

results.txt

n 10
ifelse 0.18849027999999998
table 0.20733889000000003

n 11
ifelse 0.19307480909090913
table 0.20729382727272727

n 12
ifelse 0.20221672499999999
table 0.20399962499999993

n 13
ifelse 0.20751689230769224
table 0.2013621461538461

n 14
ifelse 0.21670767857142867
table 0.1975107357142856

n 15
ifelse 0.22186927333333345
table 0.19777445333333313

n 16
ifelse 0.22301578749999984
table 0.19646908125000007

n 17
ifelse 0.2332971823529411
table 0.19414692941176442

n 18
ifelse 0.2459139055555555
table 0.19327038333333332

n 19
ifelse 0.24255543684210548
table 0.19525191578947362

n 20
ifelse 0.2588372049999997
table 0.19517728999999945

n 21
ifelse 0.26504744285714327
table 0.19126317142857172

n 22
ifelse 0.290177722727273
table 0.1923927818181813

n 23
ifelse 0.2850982608695652
table 0.18657619130434802

n 24
ifelse 0.2944755791666669
table 0.1851711708333331

n 25
ifelse 0.2965222399999999
table 0.18683115199999975

n 26
ifelse 0.3051656884615382
table 0.18965108076923143

n 27
ifelse 0.3249459555555558
table 0.1891015259259253

n 28
ifelse 0.3348370678571432
table 0.19059417500000006

n 29
ifelse 0.33812261034482805
table 0.18927325862068953

n 30
ifelse 0.3402334599999998
table 0.18482614999999972

n 31
ifelse 0.3501115806451618
table 0.18180615483870974


Process finished with exit code 0