使用ftplib.retrlines下载ftp中文本文件的前N行 [英] Download the first N rows of text file in ftp with ftplib.retrlines

问题描述

我需要从python访问ftp服务器，并下载特定文本文件的前N行.

I need to access an ftp server from python, and download the first N rows of a specific text file.

我了解了ftplib和函数目录，但是我不明白如何仅在不下载整个文件的情况下检索前N行(但是我想知道在ftp协议中是否可以做到这一点)

I read about ftplib and function retrlines, but I didn't understand how to retrieve the first N lines only without downloading the entire file (However I wonder whether that is possible in the ftp protocol)

推荐答案

您可以通过引发异常来中止文件下载.

You can abort the file download by throwing an exception.

尽管如此，您必须明确进行清理，否则将由retrlines完成.

Though then you have to explicitly do a cleanup that would otherwise by done by the retrlines.

c = 1

class TooManyLines(Exception):
    pass

contents = ""
def collectLines(s):
    global contents, c
    contents += s + "\n"
    c += 1
    if c == 5:
        raise TooManyLines()

try:
    ftp.retrlines("RETR /path/file.txt", collectLines)
except TooManyLines:
    # read/skip response
    ftp.getmultiline()

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清洁程序将复制retrlines实现，并根据需要对其进行修改.

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Cleaner would be to copy over retrlines implementation and modify it as you need.

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