python - 用python删除文件中的最后一行

Question

如何用 python 删除文件的最后一行？

输入文件示例:

hello
world
foo
bar

输出文件示例:

hello
world
foo

我创建了以下代码来查找文件中的行数 - 但我不知道如何删除特定的行号。

    try:
        file = open("file")
    except IOError:
        print "Failed to read file."
    countLines = len(file.readlines())

Answer 1

因为我经常处理许多千兆字节的文件，所以按答案中提到的循环对我来说不起作用。我使用的解决方案:

with open(sys.argv[1], "r+", encoding = "utf-8") as file:

    # Move the pointer (similar to a cursor in a text editor) to the end of the file
    file.seek(0, os.SEEK_END)

    # This code means the following code skips the very last character in the file -
    # i.e. in the case the last line is null we delete the last line
    # and the penultimate one
    pos = file.tell() - 1

    # Read each character in the file one at a time from the penultimate
    # character going backwards, searching for a newline character
    # If we find a new line, exit the search
    while pos > 0 and file.read(1) != "\n":
        pos -= 1
        file.seek(pos, os.SEEK_SET)

    # So long as we're not at the start of the file, delete all the characters ahead
    # of this position
    if pos > 0:
        file.seek(pos, os.SEEK_SET)
        file.truncate()