def _xpath_eval(xmlschema, xpath, namespaces):
    """
    Wrapper around the xpath calls in this module. Used for caching the
    results

    :param xmlschema: xmltree representing the schema
    :param xpath: str, xpath expression to evaluate
    :param namespaces: dictionary with the defined namespaces
    """
    return xmlschema.xpath(xpath, namespaces=namespaces)