pexpect python throw error - python-3.4

Question

Although this is my first attempt at using pexpect, the python3 script using pexpect is pretty simple; yet it fails.
#!/usr/bin/env python3
import sys
import pexpect
SSH_NEWKEY = r'Are you sure you want to continue connecting \(yes/no\)\?'
child = pexpect.spawn("ssh -i /user/aws/key.pem ec2-user#xxx.xxx.xxx.xxx date")
i = child.expect( [ pexpect.TIMEOUT, SSH_NEWKEY )
if i == 1:
child.sendline('yes')
print(child.before)
The SSH_NEWKEY is the only response I'm expecting, but the example showed a list containing pexpect.TIMEOUT in it so I used it.
$ ./test.py
Traceback (most recent call last):
File "/usr/local/lib/python3.4/site-packages/pexpect/spawnbase.py", line 144, in read_nonblocking
s = os.read(self.child_fd, size)
OSError: [Errno 5] Input/output error
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/usr/local/lib/python3.4/site-packages/pexpect/expect.py", line 97, in expect_loop
incoming = spawn.read_nonblocking(spawn.maxread, timeout)
File "/usr/local/lib/python3.4/site-packages/pexpect/pty_spawn.py", line 455, in read_nonblocking
return super(spawn, self).read_nonblocking(size)
File "/usr/local/lib/python3.4/site-packages/pexpect/spawnbase.py", line 149, in read_nonblocking
raise EOF('End Of File (EOF). Exception style platform.')
pexpect.exceptions.EOF: End Of File (EOF). Exception style platform.
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "./min.py", line 15, in <module>
i = child.expect( [ pexpect.TIMEOUT, SSH_NEWKEY ] )
File "/usr/local/lib/python3.4/site-packages/pexpect/spawnbase.py", line 315, in expect
timeout, searchwindowsize, async)
File "/usr/local/lib/python3.4/site-packages/pexpect/spawnbase.py", line 339, in expect_list
return exp.expect_loop(timeout)
File "/usr/local/lib/python3.4/site-packages/pexpect/expect.py", line 102, in expect_loop
return self.eof(e)
File "/usr/local/lib/python3.4/site-packages/pexpect/expect.py", line 49, in eof
raise EOF(msg)
pexpect.exceptions.EOF: End Of File (EOF). Exception style platform.
<pexpect.pty_spawn.spawn object at 0x7f70ea4fbcf8>
command: /usr/bin/ssh
args: ['/usr/bin/ssh', '-i', '/user/aws/key.pem', 'ec2-user#xxx.xxx.xxx.xxx', 'date']
searcher: None
buffer (last 100 chars): b''
before (last 100 chars): b'Fri May 6 13:50:18 EDT 2016\r\n'
after: <class 'pexpect.exceptions.EOF'>
match: None
match_index: None
exitstatus: 0
flag_eof: True
pid: 31293
child_fd: 5
closed: False
timeout: 30
delimiter: <class 'pexpect.exceptions.EOF'>
logfile: None
logfile_read: None
logfile_send: None
maxread: 2000
ignorecase: False
searchwindowsize: None
delaybeforesend: 0.05
delayafterclose: 0.1
delayafterterminate: 0.1
What am I missing?
CentOS 6.4
python 3.4.3

Answer 1

An EOF error is being raised during your expect call. This means that the response received does not match SSH_NEWKEY, and reaches end of file within the timeout period. To catch this exception, you should change your except line to read:
i = child.expect( [ pexpect.TIMEOUT, SSH_NEWKEY, pexpect.EOF)
You can then make your if more robust:
if i == 1:
child.sendline('yes')
elif i == 0:
print "Timeout"
elif i == 2:
print "EOF"
print(child.before)
This doesn't solve the reason behind why you are on receiving a response with the expected string - it's hard to know without looking at more code but it's likely because you have the response slightly wrong. If you manually type in the SSH string, you should be able to see the response you can expect, and enter this response into your code.
You can also print child.before after your expect call, or print child.read() instead of your expect call to see what is being sent back as a response.