检索从三条加到十条，为什么还得重新评估？

relevance = {
    'D1': 1, 'D2': 0, 'D3': 1, 'D4': 0,
    'D5': 0, 'D6': 1, 'D7': 0, 'D8': 1,
    'D9': 0, 'D10': 0, 'D11': 1, 'D12': 0,
}
ranked = [f'D{i}' for i in range(1, 11)]
total_relevant = sum(relevance.values())
assert len(ranked) == len(set(ranked))
assert all(doc_id in relevance for doc_id in ranked)


def measure(k):
    if type(k) is not int or not 1 <= k <= len(ranked):
        raise ValueError('k must be an integer within the ranked list')
    hits = sum(relevance[doc_id] for doc_id in ranked[:k])
    precision = hits / k
    recall = hits / total_relevant if total_relevant else None
    return hits, precision, recall


print('all relevant:', total_relevant)
for k in [3, 5, 6, 10]:
    hits, precision, recall = measure(k)
    shown = f'{recall:.1%}' if recall is not None else 'undefined'
    print(f'k={k}: hits={hits}, P@k={precision:.1%}, R@k={shown}')