Compare while-loop with break to for-loop with two-argument iter() for iterating over a large file in chunks

shasum_chunked.py

"""Compare three ways to iterate over a large file in chunks."""

import functools
import hashlib
import mmap
import os
import pathlib
import shutil
import time
import types

__all__ = ['sha256sum_while',
           'sha256sum_iter',
           'sha256sum_copyfileobj',
           'sha256sum_mmap']

PATH = pathlib.Path('spam.bin')

SIZE = 107_3741_824

CHUNK = 1_048_576

EXPECTED_RESULT = '49bc20df15e412a64472421e13fe86ff1c5165e18b2afccf160d4dc19fe68a14'


def sha256sum_while(path: os.PathLike | str, *,
                    bufsize: int = 32_768) -> str:
    s = hashlib.sha256()

    with open(path, 'rb') as f:
        while True:
            data = f.read(bufsize)
            if not data:
                break
            s.update(data)

    return s.hexdigest()


def sha256sum_iter(path: os.PathLike | str, *,
                   bufsize: int = 32_768) -> str:
    s = hashlib.sha256()

    with open(path, 'rb') as f:
        for data in iter(functools.partial(f.read, bufsize), b''):
            s.update(data)

    return s.hexdigest()


def sha256sum_copyfileobj(path: os.PathLike | str, *,
                          bufsize: int = 32_768) -> str:
    s = hashlib.sha256()

    dest = types.SimpleNamespace(write=s.update)
    with open(path, 'rb') as f:
        shutil.copyfileobj(f, dest, length=bufsize)

    return s.hexdigest()


def sha256sum_mmap(path: os.PathLike | str) -> str:
    # poor performance under PY3?
    s = hashlib.sha256()

    with open(path, 'rb')as f, mmap.mmap(f.fileno(), 0,
                                         access=mmap.ACCESS_READ) as data:
        s.update(data)

    return s.hexdigest()


if not PATH.exists():
    with PATH.open('wb') as f:
        zeros = b'\x00' * CHUNK
        for _ in range(SIZE // CHUNK):
            f.write(zeros)

for func_name in __all__:
    print(func_name)
    func = eval(func_name)
    print(func)

    start = time.perf_counter_ns()
    result = func(PATH)
    duration = (time.perf_counter_ns() - start) / 1_000_000_000

    print('result:', 'OK' if result == EXPECTED_RESULT else result)
    print('duration:', duration)
    print()