@classmethod<EOL><INDENT>def from_transport(cls, t, window_size=None, max_packet_size=None):<DEDENT>
chan = t.open_session(<EOL>window_size=window_size, max_packet_size=max_packet_size<EOL>)<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 `.Transport`.

Setting the window and packet sizes might affect the transfer speed.
The default settings in the `.Transport` class are the same as in
OpenSSH and should work adequately for both files transfers and
interactive sessions.

:param .Transport t: an open `.Transport` which is already
    authenticated
:param int window_size:
    optional window size for the `.SFTPClient` session.
:param int max_packet_size:
    optional max packet size for the `.SFTPClient` session..

:return:
    a new `.SFTPClient` object, referring to an sftp session (channel)
    across the transport

.. versionchanged:: 1.15
    Added the ``window_size`` and ``max_packet_size`` arguments.