编写Python脚本来实现最简单的FTP下载的教程

import osfrom 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()