def is_match(df, id_dict):
    """Find a rows based on exact match to identifiers.

    Arguments:
        df:
        id_dict: An identifier dictionary.

    Returns:
        loc: A Boolean index.

    """
    loc = None
    if len(df) > 0:
        for k, v in id_dict.items():
            if loc is None:
                loc = df[k] == v
            else:
                loc = loc & (df[k] == v)
    else:
        loc = []
    return loc