Quick reimplementation of OpenCV partition function in Python

from cv2_45 import cv2
import numpy as np

points = [(522, 114),
    (523, 114),
    (524, 114),
    (522, 115),
    (523, 115),
    (524, 115),
    (522, 116),
    (523, 116),
    (524, 116),
    (523, 117),
    (191, 178),
    (192, 178),
    (193, 178)]

def partition(items, predicate):
    N = len(items)

    # // The first O(N) pass: create N single-vertex trees
    parents = [-1] * N
    ranks = [0] * N

    # The main O(N^2) pass: merge connected components
    for i in range(N):
        # Find root
        root = i
        while parents[root] >= 0:
            root = parents[root]

        for j in range(N):
            if i == j or not predicate(items[i], items[j]):
                continue

            root2 = j
            while parents[root2] >= 0:
                root2 = parents[root2]

            if root != root2:
                # Unite both trees
                rank, rank2 = ranks[root], ranks[root2]
                if rank > rank2:
                    parents[root2] = root
                else:
                    parents[root] = root2
                    ranks[root2] += 1 if rank == rank2 else 0
                    root = root2
                assert parents[root] < 0

                # compress the path from node2 to root
                k = j
                while True:
                    parent = parents[k]
                    if parent < 0:
                        break
                    parents[k] = root
                    k = parent


                #compress the path from node to root
                k = i
                while True:
                    parent = parents[k]
                    if parent < 0:
                        break
                    parents[k] = root
                    k = parent

    # Final O(N) pass: enumerate classes
    labels = [0] * N
    nclasses = 0

    for i in range(N):
        root = i
        while parents[root] >= 0:
            root = parents[root]
        # re-use the rank as the class label
        if ranks[root] >= 0:
            ranks[root] = ~nclasses
            nclasses += 1
        labels[i] = ~ranks[root]

    return nclasses, labels


def predicate(point1, point2):
    threshold = 10
    return (abs(point1[0] - point2[0]) < threshold) and (abs(point1[1] - point2[1]) < threshold)

print(partition(points, predicate))