编写Python脚本来实现最简单的FTP下载的教程

访问FTP，无非两件事情：upload和download，最近在项目中需要从ftp下载大量文件，然后我就试着去实验自己的ftp操作类，如下（PS：此段有问题，别复制使用，可以参考去试验自己的ftp类！）

import os
from ftplib import FTP

class FTPSync():
 def __init__(self, host, usr, psw, log_file):
   self.host = host
   self.usr = usr
   self.psw = psw
   self.log_file = log_file

def __ConnectServer(self):
   try:
     self.ftp = FTP(self.host)
     self.ftp.login(self.usr, self.psw)
     self.ftp.set_pasv(False)
     return True
   except Exception:
     return False

def __CloseServer(self):
   try:
     self.ftp.quit()
     return True
   except Exception:
     return False

def __CheckSizeEqual(self, remoteFile, localFile):
   try:
     remoteFileSize = self.ftp.size(remoteFile)
     localFileSize = os.path.getsize(localFile)
     if localFileSize == remoteFileSize:
       return True
     else:
       return False
   except Exception:
     return None

def __DownloadFile(self, remoteFile, localFile):
   try:
     self.ftp.cwd(os.path.dirname(remoteFile))
     f = open(localFile, 'wb')
     remoteFileName = 'RETR ' + os.path.basename(remoteFile)
     self.ftp.retrbinary(remoteFileName, f.write)

if self.__CheckSizeEqual(remoteFile, localFile):
       self.log_file.write('The File is downloaded successfully to ％s' + '\n' ％ localFile)
       return True
     else:
       self.log_file.write('The localFile ％s size is not same with the remoteFile' + '\n' ％ localFile)
       return False
   except Exception:
     return False

def __DownloadFolder(self, remoteFolder, localFolder):
   try:
     fileList = []
     self.ftp.retrlines('NLST', fileList.append)
     for remoteFile in fileList:
       localFile = os.path.join(localFolder, remoteFile)
       return self.__DownloadFile(remoteFile, localFile)
   except Exception:
     return False

def SyncFromFTP(self, remoteFolder, localFolder):
   self.__DownloadFolder(remoteFolder, localFolder)
   self.log_file.close()
   self.__CloseServer()