'Create an instance of the conditional module.'

def __init__(self, *args, **kwargs):

    super(ConditionalDescriptor, self).__init__(*args, **kwargs)
    if (not self.sources_list):
        if (('sources' in self.xml_attributes) and isinstance(self.xml_attributes['sources'], basestring)):
            self.sources_list = [self.location.course_key.make_usage_key_from_deprecated_string(item) for item in ConditionalDescriptor.parse_sources(self.xml_attributes)]
