在Python中修改大型文本文件的最后一行的最有效方法

Question

我需要从超过2GB的文件中更新最后一行，这些文件由无法读取的文本行组成readlines()。目前，它可以通过逐行循环工作。但是，我想知道是否有任何编译的库可以更有效地实现这一目标？谢谢！

目前的方法

    myfile = open("large.XML")
    for line in myfile:
        do_something()

Answer 1

更新：使用ShadowRanger的答案。它更短且更健壮。

对于后代：

读取文件的最后N个字节，然后向后搜索换行符。

#!/usr/bin/env python

with open("test.txt", "wb") as testfile:
    testfile.write('\n'.join(["one", "two", "three"]) + '\n')

with open("test.txt", "r+b") as myfile:
    # Read the last 1kiB of the file
    # we could make this be dynamic, but chances are there's
    # a number like 1kiB that'll work 100% of the time for you
    myfile.seek(0,2)
    filesize = myfile.tell()
    blocksize = min(1024, filesize)
    myfile.seek(-blocksize, 2)
    # search backwards for a newline (excluding very last byte
    # in case the file ends with a newline)
    index = myfile.read().rindex('\n', 0, blocksize - 1)
    # seek to the character just after the newline
    myfile.seek(index + 1 - blocksize, 2)
    # read in the last line of the file
    lastline = myfile.read()
    # modify last_line
    lastline = "Brand New Line!\n"
    # seek back to the start of the last line
    myfile.seek(index + 1 - blocksize, 2)
    # write out new version of the last line
    myfile.write(lastline)
    myfile.truncate()