Pexpect not working at Yes/No prompt

Question

I'm using pexpect to login and run commands on a cisco router. It's getting stuck at the RSA yes/no prompt and not sending "yes". Here is a snippet of the code:

fout = file(filepath,'w')
child = pexpect.spawn('ssh %s@%s' % (username, agg))
child.logfile_read = fout
rsa_key = '\(yes\/no\)\?' 
prompt = "Password:"
i = child.expect([rsa_key,prompt,""])
if i==0:
    child.sendline('yes')
    child.expect(prompt)
    child.sendline(password)
elif i==1:
    child.sendline(password)
else:       
    child.sendline(password)

child.expect('>')
child.sendline('enable')
child.expect('Password:')
child.sendline(password)
child.expect('#')
child.sendline('terminal length 0')
child.expect('#')
child.sendline('show processes cpu history')
child.expect('#')
child.sendline('logout')

Here's the error I get:

Traceback (most recent call last):
  File "/usr/pre_check.py", line 378, in <module>
    agg_check = agg_checks(agg,username,password)
  File "/usr/pre_check.py", line 198, in agg_checks
    child.expect('>')
  File "/usr/local/lib/python2.7/dist-packages/pexpect/spawnbase.py", line 327, in expect
    timeout, searchwindowsize, async_)
  File "/usr/local/lib/python2.7/dist-packages/pexpect/spawnbase.py", line 355, in expect_list
    return exp.expect_loop(timeout)
  File "/usr/local/lib/python2.7/dist-packages/pexpect/expect.py", line 104, in expect_loop
    return self.timeout(e)
  File "/usr/local/lib/python2.7/dist-packages/pexpect/expect.py", line 68, in timeout
    raise TIMEOUT(msg)
pexpect.exceptions.TIMEOUT: Timeout exceeded.
<pexpect.pty_spawn.spawn object at 0x7f6c5e4b89d0>
command: /usr/bin/ssh
args: ['/usr/bin/ssh', 'username@router']
buffer (last 100 chars): 'TyefPiveH4nHv1dfvbL/MFbqSR+dup1U7Cn+JaDeq0.\r\nAre you sure you want to continue connecting (yes/no)? '
before (last 100 chars): 'TyefPiveH4nHv1dfvbL/MFbqSR+dup1U7Cn+JaDeq0.\r\nAre you sure you want to continue connecting (yes/no)? '
after: <class 'pexpect.exceptions.TIMEOUT'>
match: None
match_index: None
exitstatus: None
flag_eof: False
pid: 28991
child_fd: 7
closed: False
timeout: 30
delimiter: <class 'pexpect.exceptions.EOF'>
logfile: None
logfile_read: <open file 'mylogfile.txt', mode 'w' at 0x7f6c5e53ee40>
logfile_send: None
maxread: 2000
ignorecase: False
searchwindowsize: None
delaybeforesend: 0.05
delayafterclose: 0.1
delayafterterminate: 0.1
searcher: searcher_re:
    0: re.compile(">")

I have tried varius versions of the rsa_key variable with the same problem:

• Are you sure you want to continue connecting (yes/no)\\?
• Are you sure you want to continue connecting (yes/no)?
• Are you sure you want to continue connecting
• (yes/no)?
• (yes/no)\\?
• (yes/no)

Here is what it looks like when ssh'ing to the switch:

ssh username@routername
The authenticity of host 'routername (11.111.111.1)' can't be established.
RSA key fingerprint is SHA256:KCS1HKzltOwHgg+WhTsV3OTxNzxUQwN9T3Jp1lGVu00.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'routername,11.111.111.1' (RSA) to the list of known hosts.
Password: 

routername>

Answer 1

Personally I would dodge that whole bit with ssh -o StrictHostKeyChecking=no since it seems you don't care to make a decision based off of any interpretation. I'm not sure your use case for the empty string match in the list being passed to expect call, however it seems that regardless of the index, you are sending the password and expecting the prompt as if initial authentication and hostchecking is completed. The error you received shows the buffer as containing the yes/no prompt but expecting failing while expecting a > . It is possible that your password is being sent to yes no prompt and then presenting "Please type 'yes' or 'no':" which doesn't contain > causing you to time out.

Answer 2

You need to use '(?i)yes/no'. I ran into this same issue.