Sanitizes an XML field name (since it might have characters which would make it inaccessible as a python attribute).

def _sanitize_field_name(self, field_name):
        """
        Sanitizes an XML field name (since it might have characters which would make it inaccessible as a python attribute).
        """
        field_name = field_name.replace(self._field_prefix, '')
        return field_name.replace('.', '_').replace('-', '_').lower()