def iter_join(t, join_on='_'):
    """

    Convert an iterabe (``t``) to a string by joining on ``join_on``.

    :param t: any iterable.
    :type t: ``iterable``
    :param join_on: a string to join ``t`` on.
    :type join_on: ``str``
    :return: ``t`` as a string.
    :rtype: ``str``
    """
    return join_on.join(t) if isinstance(t, (list, tuple)) else t
