def get_element_by_identifier(attribute, search_string, element_tree):
    """
    Get element by attribute and string.
    :param attribute: string of attribute type
    :param search_string: identifying string to look for
    :param element_tree: element tree to look in
    :return: found element
    """
    return element_tree.find(
        '''.//*[@{attribute}='{search_string}']'''.format(attribute=attribute, search_string=search_string))