def get_by_id(xml, path, identifier):
    """
    Find a node with a specific child Identifier node.

    Parameters
    ----------
    xml : etree.Element
        Root node of XPath expression
    path : str
        XPath expression relative to `xml`
    identifier : str
        Value of child Identifier node

    Returns
    -------
    etree.Element
        node found by path with an Identifier node with value of `identifier`
    """

    return xml.xpath('{path}/Identifier[text()="{identifier}"]/..'.format(path=path, identifier=identifier))[0]