如何在Python中高效地向后读取文件？

如何使用 Python 高效地以逆序读取文件

以逆序读取文件，从最后一行开始回到开头，Python 提供了一个强大的解决方案：一个反向迭代各行的生成器函数

高效的生成器解决方案：

下面的生成器函数，reverse_readline，高效地完成了这个任务：

import os

def reverse_readline(filename, buf_size=8192):
    """A generator that returns the lines of a file in reverse order"""
    with open(filename, 'rb') as fh:
        segment = None
        offset = 0
        fh.seek(0, os.SEEK_END)
        file_size = remaining_size = fh.tell()
        while remaining_size > 0:
            offset = min(file_size, offset + buf_size)
            fh.seek(file_size - offset)
            buffer = fh.read(min(remaining_size, buf_size))
            # remove file's last "\n" if it exists, only for the first buffer
            if remaining_size == file_size and buffer[-1] == ord('\n'):
                buffer = buffer[:-1]
            remaining_size -= buf_size
            lines = buffer.split('\n'.encode())
            # append last chunk's segment to this chunk's last line
            if segment is not None:
                lines[-1] += segment
            segment = lines[0]
            lines = lines[1:]
            # yield lines in this chunk except the segment
            for line in reversed(lines):
                # only decode on a parsed line, to avoid utf-8 decode error
                yield line.decode()
        # Don't yield None if the file was empty
        if segment is not None:
            yield segment.decode()

这个函数维护偏移量并从末尾开始以反向块读取文件。它以相反的顺序生成行，同时处理最后一行可能有尾随换行符的特殊情况。

要使用此生成器，只需以二进制模式打开文件并以相反的顺序迭代各行：

for line in reverse_readline("my_file.txt"):
    # Process line in reverse order

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