该脚本实现了自动登陆cisco交换机，可在特权模式、配置模式、子配置模式间自由切换，还实现了添加、修改缺省网关的功能。当然你可以使用返回的expect对象，执行其它交换命令。

需要安装python pexect模块，该模块不支持windows，所以此脚本也就不能运行在windows下。

#!/usr/bin/python
#
#Notice:Please close domain lookup on your router or switch.

__author__="ring0"
__date__ ="$2011-6-5 18:00:00$"
__version__ ="0.3"

import sys
try:
    import pexpect
except:
    print "You must install pexpect module"
TIMEOUT=1
HOSTNAME="Router"

def exit_to_config(instance):
    '''
    Return to config mode,from config sub mode such as config-if,or multi level sub mode such as config-keychain-key.
    '''
    global TIMEOUT
    global HOSTNAME
    r_max=5
    instance.sendline('exit')
    i=instance.expect([HOSTNAME+'\(config\)#',pexpect.EOF,pexpect.TIMEOUT],TIMEOUT)
    if i==0:
        return True,"Back to config mode success."
    elif r_max<0:
        return False,"Exceed the maximum number of recursice."
    else:
        r_max=r_max-1
        exit_to_config(instance)

def login(hostip,password,hostname):
    '''
    Create pexpect instance,and login to Cisco device.
    '''
    global TIMEOUT
    global HOSTNAME
    HOSTNAME=hostname
    try:
        t=pexpect.spawn('telnet %s' % hostip)
    except:
        return False,"Can't create pexpect.spawn instance when call telnet command."
    i=t.expect(['Password:',pexpect.EOF,pexpect.TIMEOUT],TIMEOUT)
    if i==0:
        t.sendline(password)
    else:
        return False,"Connect to host failed,Please Check Router or Switch IP."
    i=t.expect([HOSTNAME+'>',pexpect.EOF,pexpect.TIMEOUT],TIMEOUT)
    if i==0:
        return t,"Login success."
    else:
        return False,"Login failed,Please check your password or hostname."

def privilege(instance,passwd=''):
    '''
    Enter privilege mode
    '''
    global TIMEOUT
    global HOSTNAME
    if not isinstance(instance,pexpect.spawn):
        return False,"Paremeter is not instance of pexpect.spawn."

    instance.sendline('')
    i=instance.expect([HOSTNAME+'#',pexpect.EOF,pexpect.TIMEOUT],TIMEOUT)
    if i==0:
        return True,"Already in privilege mode."
    if instance.isalive:
        instance.sendline('')
        i=instance.expect([HOSTNAME+'>',pexpect.EOF,pexpect.TIMEOUT],TIMEOUT)
        if i==0:
            instance.sendline('enable')
            i=instance.expect(['Password:',pexpect.EOF,pexpect.TIMEOUT],TIMEOUT)
            if i==0:
                instance.sendline(passwd)
                i=instance.expect([HOSTNAME+'#',pexpect.EOF,pexpect.TIMEOUT],TIMEOUT)
                if i==0:
                    return True,"Entered privilege mode success."
                else:
                    return False,'Enable password wrong.'
            else:
                return False,'Enable command failed'
    instance.sendline('')
    i=instance.expect([HOSTNAME+'\((.*)\)#',pexpect.EOF,pexpect.TIMEOUT],TIMEOUT)
    if i==0:
        instance.sendline('end')
        i=instance.expect([HOSTNAME+'#',pexpect.EOF,pexpect.TIMEOUT],TIMEOUT)
        if i==0:
            return True,"Back to privilege mode success."
        else:
            return False,"Back to privilege mode failed."
    return False,"Enter privilege failed."

def config(instance):
    '''
    Enter configure mode
    '''
    global HOSTNAME
    if not isinstance(instance,pexpect.spawn):
        return False,"paremeter is not instance of pexpect.spawn."

    if instance.isalive:
        instance.sendline('')
        i=instance.expect([HOSTNAME+'#',pexpect.EOF,pexpect.TIMEOUT],TIMEOUT)
        if i==0:
            instance.sendline('conf t')
            i=instance.expect([HOSTNAME+'\(config\)#',pexpect.EOF,pexpect.TIMEOUT],TIMEOUT)
            if i==0:
                return True,"Enter config mode success."
            else:
                return False,"Enter Config Mode failed from privilege mode."
    else:
        return False,'Please login first.'

    instance.sendline('')
    i=instance.expect([HOSTNAME+'\(config\)#',pexpect.EOF,pexpect.TIMEOUT],TIMEOUT)
    if i==0:
        return True,"Already in config mode."
    instance.sendline('')
    i=instance.expect([HOSTNAME+'\((.*)\)#',pexpect.EOF,pexpect.TIMEOUT],TIMEOUT)
    if i==0:
        return exit_to_config(instance)

def add_gw(instance,gw):
    '''
    Add default gateway
    '''
    global TIMEOUT
    global HOSTNAME
    if not isinstance(instance,pexpect.spawn):
        return False,"paremeter is not instance of pexpect.spawn."
    if instance.isalive:
        instance.sendline('')
        i=instance.expect([HOSTNAME+'\(config\)#',pexpect.EOF,pexpect.TIMEOUT],1)
        if i==0:
            instance.sendline('ip route 0.0.0.0 0.0.0.0 '+gw)
            return True,"Add default route success."
        else:
            return False,"This function must execute in Config Mode."
    else:
        return False,"Please login first."

def chg_gw(instance,o_gw,n_gw):
    '''
    Change default gateway
    '''
    global TIMEOUT
    global HOSTNAME
    if not isinstance(instance,pexpect.spawn):
        return False,"paremeter is not instance of pexpect.spawn."
    if instance.isalive:
        instance.sendline('')
        i=instance.expect([HOSTNAME+'\(config\)#',pexpect.EOF,pexpect.TIMEOUT],TIMEOUT)
        if i==0:
            instance.sendline('no ip route 0.0.0.0 0.0.0.0 '+o_gw)
            i=instance.expect(['No matching route to delete',pexpect.EOF,pexpect.TIMEOUT],TIMEOUT)
            if i==0:
                return False,"The old default route dons't exist."
            else:
                instance.sendline('ip route 0.0.0.0 0.0.0.0 '+n_gw)
                i=instance.expect([HOSTNAME+'\(config\)#',pexpect.EOF,pexpect.TIMEOUT],TIMEOUT)
                if i==0:
                    return True,"Change default route success."
                else:
                    return False,"Add new default route failed."
        else:
            return False,"Please enter config mode first."
    else:
        return False,"Please login first."

if __name__ == "__main__":

    route='1.1.1.5'
    password='hxsd'
    hostname='Router'
    enable='abc'

    (ret,msg)=login(route,password,hostname)
    
    if ret==False:
        sys.exit(msg)
    print msg
    telnet=ret
    (ret,msg)=privilege(telnet,enable)
    print msg
    if ret:
        (ret,msg)=config(telnet)
        print msg
        if ret:
            telnet.sendline('interface f0/0')
            (ret,msg)=config(telnet)
            print msg
            if ret:
                (ret,msg)=privilege(telnet)
                if ret:
                    print msg
            (ret,msg)=config(telnet)
            print msg
            if ret:
                print add_gw(telnet,'1.1.1.7')[1]
                print chg_gw(telnet,'1.1.1.7','1.1.1.8')[1]
            telnet.sendline('key chain abc ')
            telnet.sendline('key 1')
            (ret,msg)=config(telnet)
            print msg
            if ret:
                print privilege(telnet)[1]