shuffle random merge

#!/usr/bin/env python3


import collections
import random


def merge_random(left, right):
    choices = [0] * len(left) + [1] * len(right)
    random.shuffle(choices)
    readpositions = [iter(left), iter(right)]
    return [next(readpositions[choice]) for choice in choices]


def make_shuffle():
    sequence = [1, 2, 3, 4]
    # Step 1: Directly shuffle blocks that fit into memory
    blocks = [sequence[:2], sequence[2:]]
    for block in blocks:
        random.shuffle(block)
    # Step 2: Pairwise shuffle blocks. For more blocks, repeat
    merged_block = merge_random(*blocks)
    return merged_block


def main():
    counter = collections.Counter(
            tuple(make_shuffle()) for _ in range(1_000_000))
    for value, key in sorted((value, key) for key, value in counter.items()):
        print(value, key)


if __name__ == '__main__':
    main()