How to use function to populate variable that is in a for loop?

Question

I am a complete newb to Python and development and i'm stuck on a project.

I have a function that gets me a list of servers from our Salt Master. I am then trying to use that list inside of a for loop to connect to that server and copy my public keys to them. When I hardcode the servers it runs without issue. It looks like my variable in my for loop isnt returning anything.

Here is my For loop.

def deploy_key(key, server, username, password):
    ssh = paramiko.SSHClient()
    ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
    ssh.connect(server, username=username, password=password)
    transport = ssh.get_transport()
    session = transport.open_session()
    session.set_combine_stderr(True)
    session.get_pty()
    session = transport.open_session()
    session.set_combine_stderr(True)
    session.get_pty()
    for commands in l_commands:
        session = transport.open_session()
        session.set_combine_stderr(True)
        session.get_pty()
        session.exec_command(commands)
        stdin = session.makefile('wb', -1)
        stdout = session.makefile('rb', -1)
        stdin.write(password + '\n')
        stdin.flush()

username = "myUserName"
password = "myPassword"
server = hosts()
user = getUser()
key = getKey()
l_commands = ['sudo mkdir -p /home/%s/.ssh/' % user,'sudo chmod -R 777 /home/%s' %user,
          'sudo echo "%s" >> /home/%s/.ssh/authorized_keys' %(key, user),
          'sudo chmod 644 /home/%s/.ssh/authorized_keys' % user,
          'sudo chmod 700 /home/%s/.ssh/' % user, 'sudo chmod 755 /home/%s' %user]

for host in server:
    deploy_key(key, host, username, password)

Here is my function to get the variables

import paramiko

l_password = "myPassword"
l_host = "saltMaster.salt.com"
l_commands = "sudo salt-key -L"
l_user = "myUser"

def hosts():
    ssh = paramiko.SSHClient()
    ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
    ssh.connect(l_host, username=l_user, password=l_password)
    transport = ssh.get_transport()
    session = transport.open_session()
    session.set_combine_stderr(True)
    session.get_pty()
    session = transport.open_session()
    session.set_combine_stderr(True)
    session.get_pty()
    session.exec_command(l_commands)
    stdin = session.makefile('wb', -1)
    stdout = session.makefile('rb', -1)
    stdin.write(l_password + '\n')
    stdin.flush()

    for line in stdout.read().splitlines():
        input_line = line
        input_line = input_line.replace(b"\x1b[0;32m", b'')  # remove \x1b[1;32m
        input_line = input_line.replace(b"\x1b[0;0m", b'')  # remove \x1b[1;35m
        input_line = input_line.replace(b"\x1b[0;1;34mRejected Keys:", b'')  # remove \x1b[1;36m
        input_line = input_line.replace(b"\x1b[0;1;31mUnaccepted Keys:", b'')  # remove \x1b[1m
        input_line = input_line.replace(b"\x1b[0;1;35mDenied Keys:", b'')  # remove \x07 (BEL)
        input_line = input_line.replace(b"\x1b[0;1;32mAccepted Keys:", b'')  # remove \x07 (BEL)
        input_line = input_line.replace(b"Freedom1", b'')  # remove \x07 (BEL)

        hostsIndividual = str(input_line,"utf-8")
        return(hostsIndividual)

Before your for loop what does l_commands hold, can you print it out to make sure it's what you want ? Also for your host function why are you returning after the first for loop iteration? If it's just one iteration why need a for loop in the first place? — MooingRawr
– MooingRawr, Commented Dec 28, 2016 at 18:35
The hosts() function only ever returns a single hostsIndividual value because you have a return statement inside the for loop within it. — martineau
– martineau, Commented Dec 28, 2016 at 18:45

Wasi Ahmad · Accepted Answer · 2016-12-28 18:47:47Z

The problem is in the return statement of hosts() method.

def hosts():
    // your code goes here

    for line in stdout.read().splitlines():
        // your code goes here
        hostsIndividual = str(input_line,"utf-8")
        return(hostsIndividual)

Here loop will run only once as function will return a single String in the very first iteration of the loop. You should place the return statement outside the loop first.

def hosts():
    // your code goes here

    for line in stdout.read().splitlines():
        // your code goes here
        hostsIndividual = str(input_line,"utf-8")

    return(hostsIndividual) // returning only one host name

You also need to use a list of server names (strings) and return it from hosts() method rather returning only hostIndividual (a single String) as follows.

def hosts():
    // your code goes here

    hosts = []
    for line in stdout.read().splitlines():
        // your code goes here
        hostsIndividual = str(input_line,"utf-8")
        hosts.append(hostsIndividual) 

    return(hosts) // now returning a list of host name

Now you can iterate through the list of servers (list of Strings) returned by hosts().

for host in server:
    deploy_key(key, host, username, password)

Prune · Accepted Answer · 2016-12-28 18:42:34Z

1

Your loop returns a single string, the first input line you find. Thus, in your main program, server is a that single string, and your loop

for host in server:

iterates through the characters of that string. Try making this change to your function's loop ... instead of

for line in ...
    ...
    hostsIndividual = str(input_line,"utf-8")
    return(hostsIndividual)

Use

server_list = []
for line in ...
    ...
    hostsIndividual = str(input_line,"utf-8")
    server_list.append(hostsIndividual)

return(server_list)

This builds a list of strings, each of which is one server; after the loop is done, it returns the entire list to the main program.

answered Dec 28, 2016 at 18:42

Prune

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