Create memory view of file larger than RAM

calc_crc32.py

import mmap
import zlib
import sys
from contextlib import contextmanager

@contextmanager
def f2bytes(fname):
    with open(fname, 'rb') as f :
        with  mmap.mmap(f.fileno(), 0, access=mmap.ACCESS_READ) as m:
            mmview = memoryview(m)
            try:
                yield mmview
            finally:
                mmview.release()

def main(fname):
    with f2bytes(fname) as m:
        return zlib.crc32(m)

if __name__ == '__main__':
    n = sys.argv[1]
    print(n,'crc32 =', hex(main(n)))