看下面dir的结果，pexpect模块里面没有sendline这个方法，所以会报AttributeError.

>>> import pexpect
>>> dir(pexpect)
['EOF', 'ExceptionPexpect', 'Expecter', 'PY3', 'TIMEOUT', '__all__', '__builtins__', '__doc__', '__file__', '__name__', '__package__', '__path__', '__revision__', '__version__', 'exceptions', 'expect', 'is_executable_file', 'pty_spawn', 'run', 'runu', 'searcher_re', 'searcher_string', 'spawn', 'spawnbase', 'spawnu', 'split_command_line', 'sys', 'utils', 'which']

正确的用法示例如下：

# This connects to the openbsd ftp site and
# downloads the recursive directory listing.
import pexpect
child = pexpect.spawn('ftp ftp.openbsd.org')
child.expect('Name .*: ')
child.sendline('anonymous')
child.expect('Password:')
child.sendline('noah@example.com')
child.expect('ftp> ')
child.sendline('lcd /tmp')
child.expect('ftp> ')
child.sendline('cd pub/OpenBSD')
child.expect('ftp> ')
child.sendline('get README')
child.expect('ftp> ')
child.sendline('bye')

要在pexpect.spawn(cmd)的返回值上调用sendline方法，参考：http://pexpect.readthedocs.org/en/stable/overview.html

Pexpect on Windows
New in version 4.0: Windows support

Pexpect can be used on Windows to wait for a pattern to be produced by a child process, using pexpect.popen_spawn.PopenSpawn, or a file descriptor, using pexpect.fdpexpect.fdspawn. This should be considered experimental for now.

pexpect.spawn and pexpect.run() are not available on Windows, as they rely on Unix pseudoterminals (ptys). Cross platform code must not use these.