Question

因此，我需要能够在使用Python时从FTP服务器读取和计算行数而不将其下载到本地计算机。

我知道连接服务器的代码：

ftp = ftplib.FTP('example.com')  //Object ftp set as server address
ftp.login ('username' , 'password')  // Login info
ftp.retrlines('LIST')  // List file directories
ftp.cwd ('/parent folder/another folder/file/')  //Change file directory

我也知道计算行数的基本代码如果它已经在本地下载/存储：

with open('file') as f:  
...     count = sum(1 for line in f)  
...     print (count)

我只需要知道如何连接这两段代码而无需将文件下载到我的本地系统。

感谢任何帮助。谢谢

Answer 1

据我所知，FTP没有提供任何类型的功能来读取文件内容而不实际下载它。但是你可以尝试使用Is it possible to read FTP files without writing them using Python?之类的东西（你还没有指定你正在使用的python）

#!/usr/bin/env python
from ftplib import FTP

def countLines(s):
   print len(s.split('\n'))

ftp = FTP('ftp.kernel.org') 
ftp.login()
ftp.retrbinary('RETR /pub/README_ABOUT_BZ2_FILES', countLines)

请将此代码仅作为参考

Answer 2

有一种方法：我改编了一段我为进程csv文件“动态”创建的代码。是由生产者 - 消费者问题的方法实施的。应用此模式允许我们将每个任务分配给线程（或进程）并显示大型远程文件的部分结果。您可以根据ftp请求调整它。

下载流已保存在队列中并“即时”使用。不需要HDD额外空间和内存效率。在Fedora Core 25 x86_64上使用Python 3.5.2（vanilla）进行测试。

这是适用于ftp（over http）检索的源代码：

from threading import Thread, Event
from queue import Queue, Empty
import urllib.request,sys,csv,io,os,time;
import argparse

FILE_URL = 'http://cdiac.ornl.gov/ftp/ndp030/CSV-FILES/nation.1751_2010.csv'


def download_task(url,chunk_queue,event):

    CHUNK = 1*1024
    response = urllib.request.urlopen(url)
    event.clear()

    print('%% - Starting Download  - %%')
    print('%% - ------------------ - %%')
    '''VT100 control codes.'''
    CURSOR_UP_ONE = '\x1b[1A'
    ERASE_LINE = '\x1b[2K'
    while True:
        chunk = response.read(CHUNK)
        if not chunk:
            print('%% - Download completed - %%')
            event.set()
            break
        chunk_queue.put(chunk)

def count_task(chunk_queue, event):
    part = False
    time.sleep(5) #give some time to producer
    M=0
    contador = 0
    '''VT100 control codes.'''
    CURSOR_UP_ONE = '\x1b[1A'
    ERASE_LINE = '\x1b[2K'
    while True:
        try:
            #Default behavior of queue allows getting elements from it and block if queue is Empty.
            #In this case I set argument block=False. When queue.get() and queue Empty ocurrs not block and throws a 
            #queue.Empty exception that I use for show partial result of process.
            chunk = chunk_queue.get(block=False)
            for line in chunk.splitlines(True):
                if line.endswith(b'\n'):
                    if part: ##for treat last line of chunk (normally is a part of line)
                        line = linepart + line
                        part = False
                    M += 1
                else: 
                ##if line not contains '\n' is last line of chunk. 
                ##a part of line which is completed in next interation over next chunk
                    part = True
                    linepart = line
        except Empty:
            # QUEUE EMPTY 
            print(CURSOR_UP_ONE + ERASE_LINE + CURSOR_UP_ONE)
            print(CURSOR_UP_ONE + ERASE_LINE + CURSOR_UP_ONE)
            print('Downloading records ...')
            if M>0:
                print('Partial result:  Lines: %d ' % M) #M-1 because M contains header
            if (event.is_set()): #'THE END: no elements in queue and download finished (even is set)'
                print(CURSOR_UP_ONE + ERASE_LINE+ CURSOR_UP_ONE)
                print(CURSOR_UP_ONE + ERASE_LINE+ CURSOR_UP_ONE)
                print(CURSOR_UP_ONE + ERASE_LINE+ CURSOR_UP_ONE)
                print('The consumer has waited %s times' % str(contador))
                print('RECORDS = ', M)
                break
            contador += 1
            time.sleep(1) #(give some time for loading more records) 

def main():


    chunk_queue = Queue()
    event = Event()
    args = parse_args()
    url = args.url

    p1 = Thread(target=download_task, args=(url,chunk_queue,event,))
    p1.start()
    p2 = Thread(target=count_task, args=(chunk_queue,event,))
    p2.start()
    p1.join()
    p2.join()

# The user of this module can customized one parameter:
#   + URL where the remote file can be found.

def parse_args():
    parser = argparse.ArgumentParser()
    parser.add_argument('-u', '--url', default=FILE_URL,
                        help='remote-csv-file URL')
    return parser.parse_args()


if __name__ == '__main__':
    main()

用法

$ python ftp-data.py -u <ftp-file>

示例：

python ftp-data-ol.py -u 'http://cdiac.ornl.gov/ftp/ndp030/CSV-FILES/nation.1751_2010.csv' 
The consumer has waited 0 times
RECORDS =  16327

Github上的Csv版本：https://github.com/AALVAREZG/csv-data-onthefly

如何在不使用Python本地下载的情况下计算FTP文件中的行数

2 个答案: