def _data_format_resolver(data_format, resolver_dict):
    """Resolve a value from :attr:`resolver_dict` based on the
    :attr:`data_format`.

    Args:
        data_format (:class:`~.DataFormat` or str): The data format;
            must be a member of :class:`~.DataFormat` or a string
            equivalent.
        resolver_dict (dict): the resolving dict. Can hold any value
            for any of the valid :attr:`data_format` strings

    Returns:
        The value of the key in :attr:`resolver_dict` that matches
        :attr:`data_format`
    """
    try:
        data_format = DataFormat(data_format)
    except ValueError:
        supported_formats = ', '.join(
            ["'{}'".format(f.value) for f in DataFormat])
        raise ValueError(("'data_format' must be one of {formats}. Given "
                          "'{value}'.").format(formats=supported_formats,
                                               value=data_format))
    return (resolver_dict.get(data_format) or
            resolver_dict.get(data_format.value))