ENV variable in Python

[anandoracledba]

I have this simple code:

#!/usr/bin/env python

import sys, re, os

NAS1=os.environ['NAS1']
print 'Value of NAS1: ' + NAS1

pwdfile='NAS1/admin/data/pswds'
print 'Value of pwdfile: ' + pwdfile

When I run this code, the "pwdfile" variable doesn't pick up the "NAS1" value from 2 lines above it.

Output:
$ ./search.py
Value of NAS1: /u01/app/oracle/NAS1
Value of pwdfile: NAS1/admin/data/pswds

Expected output for 'pwdfile' = /u01/app/oracle/NAS1/admin/data/pswds

Please help me understand what I am doing wrong here. Thanks in advance.