I just implemented Graham Scan algorithm in Python 3 and have to read carefully the sort documentation.  Notice this is a good algorithm for a large audience language like Python.

Since Python 3, the old order function cmp is depicted as an old way to proceed.

But some sorting procedure require complex order like this

    def sort_by_y(p0, p1):
        return p0.x - p1.x if (p0.y == p1.y) else p0.y - p1.y
    sorted(points, key=cmp_to_key(sort_by_y))

which is less natural to implement than

    def sort_by_y(p0, p1):
        return p0.x < p1.x if (p0.y == p1.y) else p0.y < p1.y
    sorted(points, cmp=sort_by_y)

Since Python 3 we should do this

    points.sort(key=attrgetter('x'))
    points.sort(key=attrgetter('y'))

But we must take care to the chaining order !!! Here we must sort first on x then on y.

I think the documentation could explain much better how to perform complex sort and the performance of the Python sort algorithm.  Is the old way faster than the new one ???  What about short and large array ???  What happen when we sort a zillion of short array ???

Is this not equivalent to the following?

  sorted(points, key=lambda p: (p.y, p.x))

Take a look at issue 35020 which discusses multisort.

It seems to me that the sorting howto covers this topic.

If I'm reading the OP's task correctly, it isn't complex at all:

   points.sort(key=attrgetter('x', 'y'))  # x is primary key; y is secondary

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