'Get the user\'s requested mode
Args:
request_dict (`QueryDict`): A dictionary-like object containing all given HTTP POST parameters.
Returns:
The course mode slug corresponding to the choice in the POST parameters,
None if the choice in the POST parameters is missing or is an unsupported mode.'

def _get_requested_mode(self, request_dict):

    if ('verified_mode' in request_dict):
        return 'verified'
    if ('honor_mode' in request_dict):
        return 'honor'
    if ('audit_mode' in request_dict):
        return 'audit'
    else:
        return None
