如何防止 pexpect 回显密码？

默认情况下，pexpect.spawn()不会输出任何东西。但是当我指定logfile=sys.stdout它还会回显密码（例如ssh）。那么我怎样才能看到与spawned 进程没有回显密码（就像Expect (the Tcl扩展）吗）？

预期示例：

# cat expect.py
import pexpect, sys

logfile = sys.stdout if len(sys.argv) == 2 else None

ssh = pexpect.spawn('ssh foo@localhost', logfile=logfile)
ssh.delaybeforesend = 1
ssh.expect('assword:')
ssh.sendline('123456')

ssh.expect('\r\n\\$')
ssh.sendline('exit')
ssh.expect(pexpect.EOF)
ssh.wait()
# python expect.py                 <-- no output
# python expect.py stdout
foo@localhost's password: 123456   <-- the password is visible
Last login: Tue Mar 22 10:32:49 2016 from localhost
$ exit
exit
Connection to localhost closed.
#

期望示例：

# cat ssh.exp
spawn ssh foo@localhost
expect assword:
send "123456\r"
expect {\$}
send "exit\r"
expect eof
wait
# expect ssh.exp
spawn ssh foo@localhost
foo@localhost's password:          <-- the password is invisible
Last login: Tue Mar 22 10:45:03 2016 from localhost
$ exit
Connection to localhost closed.
#

只是为了让问题得到解答。功劳归于Thomas K。有关更多详细信息，请参阅问题下他的评论。

# cat foo.py
import pexpect, sys

spawn = pexpect.spawnu if sys.version_info[0] >= 3 else pexpect.spawn
ssh = spawn('ssh -t foo@localhost bash --noprofile --norc')
ssh.logfile_read = sys.stdout

ssh.expect('assword:')
ssh.sendline('123456')

ssh.expect('bash-[.0-9]+[$#]')
ssh.sendline('exit')
ssh.expect(pexpect.EOF)
ssh.wait()

# python2 foo.py
foo@localhost's password:
bash-5.1$ exit
exit
Connection to localhost closed.

# python3 foo.py
foo@localhost's password:
bash-5.1$ exit
exit
Connection to localhost closed.