def get_available_palettes(chosen_palette):
    ''' Given a chosen palette, returns tuple of those available,
        or None when not found.

        Because palette support of a particular level is almost always a
        superset of lower levels, this should return all available palettes.

        Returns:
            Boolean, None: is tty or None if not found.
    '''
    result = None
    try:
        result = ALL_PALETTES[:ALL_PALETTES.index(chosen_palette)+1]
    except ValueError:
        pass
    return result
Given a chosen palette, returns tuple of those available,
        or None when not found.

        Because palette support of a particular level is almost always a
        superset of lower levels, this should return all available palettes.

        Returns:
            Boolean, None: is tty or None if not found.