Python - 反转整个文件答案

【问题标题】：Python - Reversing a Whole FilePython - 反转整个文件
【发布时间】：2013-05-07 01:46:49
【问题描述】：

我需要能够反转整个文件，或者至少是它的内容。到目前为止我的代码是：

def reverse_file(of, rf):
     oldfile = open(of, 'r')
     reversefile = open(rf, 'w')
     filedata = oldfile.read()
     rdata = str_reverse(filedata)
     reversefile.write(rdata)
     oldfile.close()
     reversefile.close()

问题是我需要定义str_reverse，但我不确定如何创建一个反转所有内容的函数。有什么帮助吗？

【问题讨论】：

你只是想让每一行反转，还是你想将第一行与最后一行切换，还是两者兼而有之？
@NolenRoyalty 一切都应该颠倒过来，不太清楚如何去做。

标签： python file reverse

【解决方案1】：

如果你想反转整个文件，你可以用data[::-1]调用write

def reverse_file(of, rf):
    with open(of) as oldfile:
        with open(rf, "w") as reversefile:
            reversefile.write(oldfile.read()[::-1])

示例：

% cat testdata
line1
line2
line3
% cat reverse_file.py
def reverse_file(of, rf):
    with open(of) as oldfile:
        with open(rf, "w") as reversefile:
            reversefile.write(oldfile.read()[::-1])

if __name__ == "__main__":
    reverse_file("testdata", "newdata")
% python reverse_file.py
% cat newdata

3enil
2enil
1enil

【讨论】：

+1 ，with open(of) as oldfile, open(rf, "w") as reversefile: 也可以正常工作。
@AshwiniChaudhary 谢谢，我想知道如果你想要两个 withs 在同一行上会是什么语法。

【解决方案2】：

支持不适合内存的文件（基于@Darius Bacon's answer）：

import os
from io import DEFAULT_BUFFER_SIZE

def reverse_blocks(file, blocksize=DEFAULT_BUFFER_SIZE):
    """Yield blocks from the file in reverse order."""
    file.seek(0, os.SEEK_END) # move file position to the end
    position = file.tell()
    while position > 0:
        delta = min(blocksize, position)
        file.seek(position - delta, os.SEEK_SET)
        yield file.read(delta)
        position -= blocksize

# reverse input and write it to output
with open("input", "rb") as infile, open("output", "wb") as outfile:
    for block in reverse_blocks(infile):
        outfile.write(block[::-1])

【讨论】：