def mods_to_step_size(mods):
    """
    Convert a set of modifier keys to a step size.

    :param mods: Modifier keys.
    :type mods: :class:`tuple`[:class:`str`]
    :return: Step size, by name.
    :rtype: :class:`str`
    """
    if "alt" in mods:
        return "fine"

    elif "shift" in mods:
        return "coarse"

    return "medium"