attribute error

[M.N.A.Smadi]

HI;

I am  having the following error.  I am using someone else's code and 
all they are doing is pass an argv to a function then

def execute_action(manager, argv):
    method_name = argv.pop(0).lower()


and am getting this strange error.
AttributeError: 'str' object has no attribute 'pop'

am using Python 2.3.4 and am importing the following libraries:

import sys, os, inspect
from Asterisk import Manager, BaseException, Config
import Asterisk.Util

but i always thought that something like this will be standard stuff.  
Any ideas?

thanks
moe smadi