heapq.py 文件源码

def nlargest(n, iterable, key=None):
    """Find the n largest elements in a dataset.

    Equivalent to:  sorted(iterable, key=key, reverse=True)[:n]
    """

    # Short-cut for n==1 is to use max() when len(iterable)>0
    if n == 1:
        it = iter(iterable)
        head = list(islice(it, 1))
        if not head:
            return []
        if key is None:
            return [max(chain(head, it))]
        return [max(chain(head, it), key=key)]

    # When n>=size, it's faster to use sorted()
    try:
        size = len(iterable)
    except (TypeError, AttributeError):
        pass
    else:
        if n >= size:
            return sorted(iterable, key=key, reverse=True)[:n]

    # When key is none, use simpler decoration
    if key is None:
        it = izip(iterable, count(0,-1))                    # decorate
        result = _nlargest(n, it)
        return map(itemgetter(0), result)                   # undecorate

    # General case, slowest method
    in1, in2 = tee(iterable)
    it = izip(imap(key, in1), count(0,-1), in2)             # decorate
    result = _nlargest(n, it)
    return map(itemgetter(2), result)                       # undecorate