seems to me the whole `HandlePermissionList(permission_list):` can be simplify to
```
regex_permission = re.compile(r'^[a-zA-Z\.]*$')
for permission in permission_list:
  if not regex_permission.match(permission):
    print 'Error: invalid permission field %s, only alphabets and "." are allowed' % permission
return ':'.join(permission_list)
```