<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _parse_roles(self):
 """ Generate a dictionary for configured roles from oslo_config. Due to limitations in ini format, it's necessary to specify roles in a flatter format than a standard dictionary. This function serves to transform these roles into a standard python dictionary. """

        roles = {}
        for keystone_role, flask_role in self.config.roles.items():
            roles.setdefault(flask_role, set()).add(keystone_role)
        return roles