蓄水池采样python实现

import random

def sample(iterable, n):
    """
    Returns @param n random items from @param iterable.
    """
    reservoir = []
    for t, item in enumerate(iterable):
        if t < n:
            reservoir.append(item)
        else:
            m = random.randint(0,t)
            if m < n:
                reservoir[m] = item
    return reservoir