Need little assistance with pexpect interaction

Question

Need little assistance with making this code work with pexpect module.

This code executes git pull by logging into a server and then downloads the latest code (if upgrade is available) or just sends out a messages saying "Already up-to-date."

The code actually idenfies the password screen but does not identify the text "already up-to-date"

not sure if I'm missing anything here.

A snippet from the code is:

        p = pexpect.spawn('git pull',cwd = comp_dir,maxread = 10000, timeout = 100)
        i = p.expect(['password:','Already up-to-date.',pexpect.EOF])
        if i == 0:
            output_lines = p.before
            output_line_list = output_lines.split('\r\n')
            for line in output_line_list: print line
            count = 0
            p.sendline(pwd)
            while count < 3:  **# The server in case of unsuccessful login asks for password thrice so this check...  (not sure if there is a better way of achieving this)**
                try:
                    output = p.expect('Permission denied')
                    count+=1
                    p.sendline(pwd)
                    p.logfile = sys.stdout
                except:
                    print 'Successful Login !!!! ------'
                    p.expect('Already up-to-date',timeout=None)
                    count = 3
        if i == 1:
            output_lines = p.before
            output_line_list = output_lines.split('\r\n')
            for line in output_line_list: print line
            p.expect(pexpect.EOF)

Any help is greatly appreciated.

Thanks, -Vijay

score 1 · Accepted Answer · answered Jul 02 '12 at 16:06

This logic seems to be a bit incorrect.

At first: you are expecting from a set of prompts

i = p.expect(['password:','Already up-to-date.',pexpect.EOF])

Which works correctly as password prompt is first to be sent. Then even if you receive the prompt - 'Already up-to-date.'

you have altered pexpect to check for 'password denied'

output = p.expect('Permission denied')

I believe that any point only one of the expect lines are active. Also you can not set expectations after a prompt has occurred.

You have to alter the script to sequentially check on the expected lines

i = p.expect(['password:','Already up-to-date.','Permission denied', pexpect.EOF])
if i == 0:
   .... send password
   i = p.expect(['password:','Already up-to-date.','Permission denied', pexpect.EOF])
if i == 2:
   .... send password
   i = p.expect(['password:','Already up-to-date.','Permission denied', pexpect.EOF])
if i == 1:
   .... print "already updated"
   i = p.expect(['password:','Already up-to-date.','Permission denied', pexpect.EOF])
if i == 3:
   .... print output

Basically, you have at any point only one active expect command active. if you are expecting a line "xyz" and it receives "123". It will just time out waiting for "xyz".

Hi Sir, One quick question on this logic.. When user enters gives password it gets into the condition i == 2: and after 3 attempts how does it come out? does it trigger out EOF after 3 attempts? I dont think it tirggers EOF as I dont see the print statement given on the condition i==3 — user596922, Jul 04 '12 at 12:41
@user596922: EOF should come after the password has been supplied. Can you try making it sequential — pyfunc, Jul 04 '12 at 17:17

Need little assistance with pexpect interaction

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