    #! /usr/bin/python

    import posix
    from string import splitfields

    def userinfo(filename):
      """
      This function returns the list of users
      and a table containing users and their passwords
      """
      users, table = [], {}
      file = open(filename, 'r')
      for line in file.readlines():
        [name, password] = splitfields(line, ':')[:2]
        users.append(name)
        table[name] = password
      return users, table

    def main():
      for filename in ('/etc/passwd', 'etc/passwd.bak'):
        try:
          users, table = userinfo(filename)
          print table.keys()[3:7], table['postgres']
          posix.system('ls -al ' + filename)
        except:
          print 'File "' + filename + '" not found!'

    main()