code: def exists(self, path, mtime=None):
          
          self._connect()
  
          if self.sftp:
              exists = self._sftp_exists(path, mtime)
          else:
              exists = self._ftp_exists(path, mtime)
  
          self._close()
  
          return exists
docs: Return `True` if file or directory at `path` exist, False otherwise.
  
          Additional check on modified time when mtime is passed in.
  
          Return False if the file's modified time is older mtime.