Python Pexpect模块：程序在从Eclipse执行时有效，但是如果从Bash执行则会发生超时？

Question

我在Python中使用Pexpect编写了以下脚本：

该程序使用Pexpect模块自动与SSH服务器建立SSH会话。

import pexpect
import argparse

PROMPT = ['# ', '>>> ', '> ', '\$ ']

def send_command(child, cmd, password):
    child.sendline(cmd)
    ret = child.expect(PROMPT + ['password'])
    if ret < len(PROMPT):
        print(child.before)
    else:
        child.sendline(password)
        child.expect(PROMPT)
        print(child.before)

def connect(user, host, password):
    ssh_newkey = 'Are you sure you want to continue connecting'
    passwd = '[P|p]assword'
    connStr = 'ssh ' + user + '@' + host
    child = pexpect.spawn(connStr)
    ret = child.expect([pexpect.TIMEOUT, ssh_newkey, passwd])
    if ret == 0: # timeout
        print('[-] Error Connecting')
        return
    if ret == 1: # new key
        child.sendline('yes')
        ret = child.expect([pexpect.TIMEOUT, passwd])
    if ret == 0: # timeout
        print('[-] Error Connecting')
        return
    child.sendline(password)
    child.expect(PROMPT)
    return child

def main():
    parser = argparse.ArgumentParser(description='SSH-client')
    parser.add_argument('user', help='SSH-user')
    parser.add_argument('host', help='SSH-host')
    parser.add_argument('password', help='SSH-password')
    parser.add_argument('-c', '--command', default='sudo cat /etc/shadow', help='command to execute')
    args = parser.parse_args()
    child = connect(args.user, args.host, args.password)
    send_command(child, args.command, args.password)

if __name__ == '__main__':
    main()

在Eclipse和Bash shell中使用相同的命令行参数，我会得到不同的结果：

使用Eclipse一切都按预期工作，程序终止于命令输出。但是，shell给出了以下超时错误：

Traceback (most recent call last):
  File "/usr/local/lib/python3.4/dist-packages/pexpect/__init__.py", line 1535, in expect_loop
    c = self.read_nonblocking(self.maxread, timeout)
  File "/usr/local/lib/python3.4/dist-packages/pexpect/__init__.py", line 968, in read_nonblocking
    raise TIMEOUT('Timeout exceeded.')
pexpect.TIMEOUT: Timeout exceeded.

During handling of the above exception, another exception occurred:

    Traceback (most recent call last):
      File "ssh_bot.py", line 46, in <module>
        main()
      File "ssh_bot.py", line 42, in main
        child = connect(args.user, args.host, args.password)
      File "ssh_bot.py", line 32, in connect
        child.expect(PROMPT)
      File "/usr/local/lib/python3.4/dist-packages/pexpect/__init__.py", line 1451, in expect
        timeout, searchwindowsize)
      File "/usr/local/lib/python3.4/dist-packages/pexpect/__init__.py", line 1466, in expect_list
        timeout, searchwindowsize)
      File "/usr/local/lib/python3.4/dist-packages/pexpect/__init__.py", line 1568, in expect_loop
        raise TIMEOUT(str(err) + '\n' + str(self))
    pexpect.TIMEOUT: Timeout exceeded.
    <pexpect.spawn object at 0x7f7e517406a0>
    version: 3.3
    command: /usr/bin/ssh
    args: ['/usr/bin/ssh', 'nlykkei@127.0.0.1']
    searcher: <pexpect.searcher_re object at 0x7f7e51740780>
    buffer (last 100 chars): b': Tue Aug 11 12:32:35 2015 from localhost\r\r\n\x1b[01;32mnlykkei@nlykkei-ThinkPad-X200s\x1b[01;34m ~ $\x1b[00m '
    before (last 100 chars): b': Tue Aug 11 12:32:35 2015 from localhost\r\r\n\x1b[01;32mnlykkei@nlykkei-ThinkPad-X200s\x1b[01;34m ~ $\x1b[00m '
    after: <class 'pexpect.TIMEOUT'>
    match: None
    match_index: None
    exitstatus: None
    flag_eof: False
    pid: 4093
    child_fd: 3

导致此错误的原因是什么，为什么我不能使用相同的命令行参数从Eclipse和Bash获得相同的结果？

谢谢！