code: def get_filesize(self, filename):
          
          result = []
  
          def dir_callback(val):
              result.append(val.split()[4])
  
          self._ftp.dir(filename, dir_callback)
          return result[0]
docs: Returns the filesize of a file
  
          :param filename: the full path to the file on the server.
          :type filename: string
  
          :returns: string representation of the filesize.