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()