[mod_python] About authentication

I'm trying to implement custom authentication using authenhandler.
I want to save user info and password in encrypted file that other users
can only read. So I've tried to use md5.new('password').hexdigest().
'password' is a variable that stores password using 
req.get_basic_auth_pw().

When I've tried to load restricted page, I got error saying 'password'
variable is not read-only buffer, but None. I can use direct comparison
of username and password with string as to the mod_python document, but I
can't use it in a function that accepts string as a argument.

Any comment or help would be appreciated.
mod_python is 2.7.2.