编写Python脚本来实现最简单的FTP下载的教程

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()