python - 按另一个日期列表拆分日期列表

Question

我在网络中有许多节点。节点每小时发送一次状态信息以表明它们还活着。所以我有一个节点列表和它们最后存活的时间。我想绘制随时间变化的事件节点数。

节点列表按它们最后一次存活的时间排序，但我想不出一个很好的方法来计算每个日期有多少存活。

from datetime import datetime, timedelta

seen = [ n.last_seen for n in c.nodes ] # a list of datetimes
seen.sort()
start = seen[0]
end = seen[-1]

diff = end - start
num_points = 100

step = diff / num_points

num = len( c.nodes )

dates = [ start + i * step for i in range( num_points ) ]

基本上我想要的是

alive = [ len([ s for s in seen if s > date]) for date in dates ]

但这并不是很有效。解决方案应该利用 seen 列表已排序这一事实，而不是针对每个日期遍历整个列表。

Answer 1

这个生成器只遍历列表一次:

def get_alive(seen, dates):
    c = len(seen)
    for date in dates:
        for s in seen[-c:]:
            if s >= date:      # replaced your > for >= as it seems to make more sense
                yield c
                break
            else:
                c -= 1