# $language = "python"
# $interface = "1.0"
import sys
import re

# Your hosts file should just be a list of IP's, each on its own line
HOSTSFILE = 'path_toyour_hosts_file.txt'
USER = 'username'
PASS = 'password'
ENABLEP = 'enablepassword'
NEW_HELPER_CMD = 'ip helper-address x.x.x.x'

def Wait():
    # Wait for a prompt
    while True:
        if not crt.Screen.WaitForCursor(1):
            break
def Get_prompt():
    row = crt.Screen.CurrentRow
    prompt = crt.Screen.Get(row, 0, row, crt.Screen.CurrentColumn - 1).strip()
    return prompt
def Get_list_from_file(file_path):
    f = open(file_path, 'r')
    hostlist = f.readlines()
    f.close()
    return hostlist
def Log_in(host):
    login_command = '/SSH2 /L {0} /PASSWORD {1} {2}'.format(USER, PASS, host)
    try:
        crt.Session.Connect(login_command)
        crt.Session.Synchronous = True
        Wait()
        return True
    except:
        # More specific except clauses needed
        # For specific error conditions, add corresponding error messages
        return False
def Exec_mode():
    prompt = Get_prompt()
    tries = 0
    # Enter priveleged exec mode if not already there
    while tries > 4:
        if re.search(r'#$', prompt):
            break
        elif re.search(r'[>]$', prompt):
            crt.Screen.Send('enablen')
            Wait()
            prompt = Get_prompt()
            if re.search(r'Password:', prompt):
                crt.Screen.Send('{0}n'.format(ENABLEP))
                Wait()
        elif re.search(r')$', prompt):
            crt.Screen.Send('endn')
            Wait()
        tries += 1
    if tries >= 4:
        # Add an error code stating that exec_mode failed
        return False
    else:
        return True
def Config_mode():
    prompt = Get_prompt()
    if re.search(r'#$', prompt):
        crt.Screen.Send('config tn')
        Wait()
    else:
        b = Exec_mode()
        if b:
            crt.Screen.Send('config tn')
            Wait()
    prompt = Get_prompt()
    if re.search(r')$', prompt):
        return True
    else:
        return False
def Pull_and_parse_config():
    Wait()
    crt.Screen.Send('term len 0n')
    Wait()
    prompt = Get_prompt()
    # Output the runnning config
    crt.Screen.Send(r'sh running-confign')
    crt.Screen.WaitForString(r'n')
    # Capture config output to string var 'config'
    # Note: If there is any duplicate of the 'prompt' string in the config, it will stop the
    # capture prematurely
    config = crt.Screen.ReadString(prompt)
    Wait()
    # Split the captured config into a list, containing the interface string, old ip helper string, and
    # remaining config. Will capture each interface on the device that currently has an ip helper command
    # Note: this only captures the first ip helper command on each interface
    configlist = re.split(r'(interface [^n]+?)n[^!]*?(ip helper-address .+?)n', config, flags=re.DOTALL)
    if len(configlist) > 1:
        configlist.pop(0)
        return configlist
    else:
        # add message stating no interfaces matched
        return False
def Update_config(configlist):
    # For each interface with an ip helper command, remove old command and add new helper command
    while len(configlist) > 2:
        int_id = configlist.pop(0)
        old_helper_cmd = configlist.pop(0)
        if re.search(r'interface .+', int_id) and re.search(r'ip helper-address .+', old_helper_cmd):
            Enter_config_mode()
            # Here is where you actually update the config
            # If you don't want to remove old helper command, remove "no {1}n" from the following string
            crt.Screen.Send('{0}n no {1}n {2}n'.format(int_id, old_helper_cmd, NEW_HELPER_CMD))
            Wait()
            return True
        elif not re.search(r'interface .+', int_id):
            # add error message stating invalid interface id
            return False
        else:
            # add error message stating invalid ip helper command
            return False
def Main():
    hostfile = Get_list_from_file(HOSTSFLIE)
    for host in hostfile:
        ok = Log_in(host)
        if not ok:
            # add error message stating login failed
            continue
        ok = Exec_mode()
        if not ok:
            # add error message here
            continue
        configlist = Pull_and_parse_config()
        if not configlist:
            # add error message stating config capture failed
        ok = Update_config(configlist)
        if not ok:
            # add error message stating config update failed
        else:
            # add success message stating config on host successfully updated

Main()