This is an example on how to build a decorator that reauthenticates with vCenter in case the session times out

vc_reconnect.py

#!/usr/bin/env python
# coding=utf-8
#
# Copyright © 2016 VMware, Inc. All Rights Reserved.
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__author__ = 'yfauser'

from pyVim import connect
from pyVmomi import vim
import ssl
import atexit
import time
from functools import wraps


vchost = 'vc.yves.local'
user = '[email protected]'
pwd = 'vmware'
searched_vm = '10.10.10.90'


VIM_TYPES = {'datacenter': [vim.Datacenter]}


def reauth():
    def reauth_decorator(f):
        @wraps(f)
        def function_reauth(*args):
            if args[0]['content'].sessionManager.currentSession:
                print '#### Session is still active'
                return  f(*args)
            else:
                print '#### Session timed out, reconnecting'
                args[0]['content'].sessionManager.Login(userName=user, password=pwd)
                return  f(*args)
        return function_reauth
    return reauth_decorator


def connect_to_api(vchost, user='root', pwd='vmware'):
    if hasattr(ssl, 'SSLContext'):
        context = ssl.SSLContext(ssl.PROTOCOL_SSLv23)
        context.verify_mode = ssl.CERT_NONE
    else:
        context = None
    if context:
        service_instance = connect.SmartConnect(host=vchost, user=user, pwd=pwd, sslContext=context)
    else:
        service_instance = connect.SmartConnect(host=vchost, user=user, pwd=pwd)

    atexit.register(connect.Disconnect, service_instance)

    return service_instance.RetrieveContent()

@reauth()
def get_vm_by_ip(vccontent, ip):
    return vccontent['content'].searchIndex.FindByIp(None, ip, True)

@reauth()
def get_vm_name(vccontent, vm):
    return vm.name

def test_loop(vccontent):
    while True:
        vm = get_vm_by_ip(vccontent, searched_vm)
        print vm.name
        time.sleep(10800)

def main():
    content = connect_to_api(vchost, user=user, pwd=pwd)
    vccontent = {'content': content, 'user': user, 'pwd': pwd}
    test_loop(vccontent)

if __name__ == '__main__':
    main()