转换成字典/类型列表，包含字符串列表的字符串列表？

下面有一堆乱七八糟的东西，但是其中的核心算法solution()似乎还不错。我不能说我喜欢sentinel那里，但是...这使其他一切都整齐了。

https://repl.it/@altendky/ChartreuseWeightyRoot-10

import functools
import itertools
import random
import string

import attr
import toolz


@attr.s(frozen=True)
class Example:
    source = attr.ib()
    target = attr.ib()
    group_handler = attr.ib()


def random_example():
    a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u, v, w, x, y, z = tuple(
        (round(abs(random.random()) ** 10, 4)
        if random.randint(0, 1) % 2 == 0
        else random.randint(20, 50)
        if random.randint(0, 1) % 2 == 0
        else ('foo', 'bar', 'can', 'haz', 'bzr')[random.randint(0, 4)])
            for c in string.ascii_lowercase)

    l1 = [a, b, c, d, e, f, g, [h, i, j, k],
        l, m, n, [o, p, q, r, [s, t, u, v, w, x, y, z], a, b], c, d, e]

    auauughhghhhh = [
        {f'{a}_key': a, f'{a}_val': b,
        f'{c}_key': c, f'{c}_val': d,
        f'{e}_key': e, f'{e}_val': f},
        g,
        [
            {f'{h}_key': h, f'{h}_val': i,
            f'{j}_key': j, f'{j}_val': k}
        ],
        {f'{l}_key': l, f'{l}_val': m},
        n,
        [
            {f'{o}_key': o, f'{o}_val': p,
            f'{q}_key': q, f'{q}_val': r},
            [
                {f'{s}_key': s, f'{s}_val': t,
                f'{u}_key': u, f'{u}_val': v,
                f'{w}_key': w, f'{w}_val': x,
                f'{y}_key': y, f'{y}_val': z}
            ],
            {f'{a}_key': a, f'{a}_val': b}
        ],
        {f'{c}_key': c, f'{c}_val': d},
        e
    ]

    g = lambda k,v: {'{}_key'.format(k): k, '{}_val'.format(k): v}

    return Example(
        source=l1,
        target=auauughhghhhh,
        group_handler=functools.partial(process_group, paired_sequence_handler=lambda s: build_dict_by_update(s, g)),
    )


def process_group(group, paired_sequence_handler):
    processed_group = []

    if len(group) == 0:
        return processed_group

    odd = (len(group) % 2) != 0
    raw_pairs = group[:-1] if odd else group
    pairs = toolz.partition_all(2, raw_pairs)
    result = paired_sequence_handler(pairs)

    processed_group.append(result)

    if odd:
        processed_group.append(group[-1])

    return processed_group


def build_dict_by_update(sequence, pair_handler):
    result = {}
    for pair in sequence:
        result.update(pair_handler(*pair))

    return result


examples = [
    Example(
        source=['foo', 'bar', ['can', 'haz']],
        target=[{'key': 'foo', 'val': 'bar'}, [{'key': 'can', 'val': 'haz'}]],
        group_handler=functools.partial(process_group, paired_sequence_handler=lambda s: build_dict_by_update(s, lambda k,v: {'key': k, 'val': v})),
    ),
    random_example(),
]


def solution(source, group_handler):
    built = []
    group = []

    sentinel = object()

    for value in itertools.chain(source, [sentinel]):
        if not isinstance(value, list) and value is not sentinel:
            group.append(value)
            continue

        built.extend(group_handler(group))
        group = []

        if value is sentinel:
            break

        result = solution(
            source=value,
            group_handler=group_handler,
        )
        built.append(result)

    return built



for example in examples:
    result = solution(
        source=example.source,
        group_handler=example.group_handler,
    )

    succeeded = result == example.target

    print('?', succeeded)

    if not succeeded:
        print('?  ', example.target)
        print('?  ', result)