Python之FTP多线程下载文件之多线程分块下载文件

Python中的ftplib模块用于对FTP的相关操作，常见的如下载，上传等。使用python从FTP下载较大的文件时，往往比较耗时，如何提高从FTP下载文件的速度呢？多线程粉墨登场，本文给大家分享我的多线程下载代码，需要用到的python主要模块包括：ftplib和threading。

首先讨论我们的下载思路，示意如下：

1. 将文件分块，比如我们打算采用20个线程去下载同一个文件，则需要将文件以二进制方式打开，平均分成20块，然后分别启用一个线程去下载一个块：

 1 def setupThreads(self, filePath, localFilePath, threadNumber = 20):
 2     """
 3     set up the threads which will be used to download images
 4     list of threads will be returned if success, else
 5     None will be returned
 6     """
 7     try:
 8         temp = self.ftp.sendcmd('SIZE ' + filePath)
 9         remoteFileSize = int(string.split(temp)[1])
10         blockSize = remoteFileSize / threadNumber
11         rest = None
12         threads = []
13         for i in range(0, threadNumber - 1):
14             beginPoint = blockSize * i
15             subThread = threading.Thread(target = self.downloadFileMultiThreads, args = (i, filePath, localFilePath, beginPoint, blockSize, rest,))
16             threads.append(subThread)
17             
18         assigned = blockSize * threadNumber
19         unassigned = remoteFileSize - assigned
20         lastBlockSize = blockSize + unassigned
21         beginPoint = blockSize * (threadNumber - 1)
22         subThread = threading.Thread(target = self.downloadFileMultiThreads, args = (threadNumber - 1, filePath, localFilePath, beginPoint, lastBlockSize, rest,))
23         threads.append(subThread)
24         return threads
25     except Exception, diag:
26         self.recordLog(str(diag), 'error')
27         return None

其中的downloadFileMultiThreads函数如下：

 1 def downloadFileMultiThreads(self, threadIndex, remoteFilePath, localFilePath, 
 2                                  beginPoint, blockSize, rest = None):
 3     """
 4     A sub thread used to download file
 5     """
 6     try:
 7         threadName = threading.currentThread().getName()
 8         # temp local file
 9         fp = open(localFilePath + '.part.' + str(threadIndex), 'wb')
10         callback = fp.write
11         
12         # another connection to ftp server, change to path, and set binary mode
13         myFtp = FTP(self.host, self.user, self.passwd)
14         myFtp.cwd(os.path.dirname(remoteFilePath))
15         myFtp.voidcmd('TYPE I')
16         
17         finishedSize = 0
18         # where to begin downloading
19         setBeginPoint = 'REST ' + str(beginPoint)
20         myFtp.sendcmd(setBeginPoint)
21         # begin to download
22         beginToDownload = 'RETR ' + os.path.basename(remoteFilePath)
23         connection = myFtp.transfercmd(beginToDownload, rest)
24         readSize = self.fixBlockSize
25         while 1:
26             if blockSize > 0:
27                 remainedSize = blockSize - finishedSize
28                 if remainedSize > self.fixBlockSize:
29                     readSize = self.fixBlockSize
30                 else:
31                     readSize = remainedSize
32             data = connection.recv(readSize)
33             if not data:
34                 break
35             finishedSize = finishedSize + len(data)
36             # make sure the finished data no more than blockSize
37             if finishedSize == blockSize:
38                 callback(data)
39                 break
40             callback(data)
41         connection.close()
42         fp.close()
43         myFtp.quit()
44         return True
45     except Exception, diag:
46         return False

2. 等待下载完成之后我们需要对各个文件块进行合并，合并的过程见本系列之二：Python之FTP多线程下载文件之分块多线程文件合并

感谢大家的阅读，希望能够帮到大家！

Published by Windows Live Writer!