您可以使用 bisect module和 collections.Counter ：

 >&gt ;> import bisect 
>>>>从集合导入计数器
>>>>计数器（x [bisect.bisect_left（x，item）] for y）
计数器（{10：3，30：2，20：1}）
 / pre> 
If my x list and y list are:
x = [10,20,30]
y = [1,2,3,15,22,27]
I'd like a return value to be a dictionary that has a count of the elements that were less than the x value:
{
    10:3,
    20:1,
    30:2,
}
I have a very large list, so I was hoping there was a better way to do it that didn't involve a slow nested for loop.  I've looked at collections.Counter and itertools and neither seem to offer a way of grouping. Is there a built-in that can do this?
You can use the bisect module and collections.Counter:
>>> import bisect
>>> from collections import Counter
>>> Counter(x[bisect.bisect_left(x, item)] for item in y)
Counter({10: 3, 30: 2, 20: 1})