def _check_suffix(path: str) -> str:
    """Checks that file is a .csv or .tsv file, and returns which sep to use

    Args:
        path: File path

    Returns: sep
        Sep to use for parsing

    """

    if path[-4:] == ".tsv":
        return "\t"
    if path[-4:] == ".csv":
        return ","
    raise ValueError("File must be .csv or .tsv")