def text_y(lines, font_size=12):
    """Return a list of lines positions according to how many lines are available

    Doctest:

    .. doctest::

        >>> text_y(0)
        [0]
        >>> text_y(1)
        [0]
        >>> text_y(2)
        [-6, 6]
        >>> text_y(3)
        [-12, 0, 12]
        >>> text_y(4)
        [-18, -6, 6, 18]
        >>> text_y(5)
        [-24, -12, 0, 12, 24]
        >>> text_y(6)
        [-30, -18, -6, 6, 18, 30]
        >>> text_y(7)
        [-36, -24, -12, 0, 12, 24, 36]
    """
    if lines < 2:
        return [0]
    extra = (lines // 2 - 1) * font_size
    final = font_size + extra
    if lines % 2 == 0:
        final = font_size // 2 + extra
    return list(range(-final, final + 1, font_size))
