二進位制檔案記憶體對映

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# 對二進位制檔案做記憶體對映
# 使用 mmap 模組對檔案進行記憶體有對映操作
import mmap
import os.path


def memory_map(filename, access=mmap.ACCESS_WRITE):
    """

    :param filename:
    :param access: mmap.ACCESS_WRITE: 讀寫
                   mmap.ACCESS_READ:  只讀
                   mmap.ACCESS_COPY: 更改不會儲存到原檔案
    :return:
    """
    size = os.path.getsize(filename)
    fd = os.open(filename, os.O_RDWR)
    return mmap.mmap(fd, size, access=access)


# make test data
size = 100000
with open("data", "wb") as f:
    f.seek(size - 1)
    f.write(b"\x00")

# test
with memory_map("data") as m:
    print(len(m))  # 100000
    print(m[:10])  # b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'
    print(m[0])  # 0
    m[0:11] = b"Hello World"

# verify
with open("data", "rb") as f:
    print(f.read(11))  # b'Hello World'