def from_transport(cls, t):
chan = t.open_session()<EOL>if chan is None:<EOL><INDENT>return None<EOL><DEDENT>chan.invoke_subsystem('<STR_LIT>')<EOL>return cls(chan)<EOL>
Create an SFTP client channel from an open L{Transport}.

@param t: an open L{Transport} which is already authenticated
@type t: L{Transport}
@return: a new L{SFTPClient} object, referring to an sftp session
    (channel) across the transport
@rtype: L{SFTPClient}