def plot_circle(x0, y0, radius):
    """Return a list of the points around a circle."""
    result = []
    f = 1 - radius
    ddf_x = 1
    ddf_y = -2 * radius
    x = 0
    y = radius
    result.append((x0, y0 + radius))
    result.append((x0, y0 - radius))
    result.append((x0 + radius, y0))
    result.append((x0 - radius, y0))

    while x < y:
        if f >= 0:
            y -= 1
            ddf_y += 2
            f += ddf_y
        x += 1
        ddf_x += 2
        f += ddf_x
        result.append((x0 + x, y0 + y))
        result.append((x0 - x, y0 + y))
        result.append((x0 + x, y0 - y))
        result.append((x0 - x, y0 - y))
        result.append((x0 + y, y0 + x))
        result.append((x0 - y, y0 + x))
        result.append((x0 + y, y0 - x))
        result.append((x0 - y, y0 - x))

    return result