ATTR and GET_ATTR can have one of 'raw', 'enc' and 'hash' fields.
    This method checks which of them presents and return it's name
    and value in it.

def _extract_attr_typed_value(txn_data):
    """
    ATTR and GET_ATTR can have one of 'raw', 'enc' and 'hash' fields.
    This method checks which of them presents and return it's name
    and value in it.
    """
    existing_keys = [key for key in ALL_ATR_KEYS if key in txn_data]
    if len(existing_keys) == 0:
        raise ValueError("ATTR should have one of the following fields: {}"
                         .format(ALL_ATR_KEYS))
    if len(existing_keys) > 1:
        raise ValueError("ATTR should have only one of the following fields: {}"
                         .format(ALL_ATR_KEYS))
    existing_key = existing_keys[0]
    return existing_key, txn_data[existing_key]