How can I only look at only a certain range within a sorted list in Python?

I have sorted lists of starting times and ending times. I also have a very large sorted list of times, t.

Right now, I am doing the extremely slow:

for start, end in zip(startTimes, endTimes):

    for time in t:
 
        if start <= t <= end:
            do something

This looks at each element in t every single time. I know I can reduce this by making some elifs for whether or not t < start or end < t, but there must be a way to take advantage of the lists being sorted.

>Solution :

Suppose you have a 1,000,000 day interval in list t:

import datetime as dt 

st=dt.datetime(1990, 1, 1)
t=[st]
for i in range(1_000_000):
    t.append(t[-1]+dt.timedelta(days=1))

>>> t[-1]
4727-11-29 00:00:00   # if man is still alive...

You can use itertools groupby to find sub intervals:

from itertools import groupby   
x=dt.datetime(2040,2,2)
y=dt.datetime(2040,2,6) 
for k,v in groupby(t, key=lambda d: x<=d<=y):
    if k:
        print(list(v))

Prints:

[datetime.datetime(2040, 2, 2, 0, 0), datetime.datetime(2040, 2, 3, 0, 0), datetime.datetime(2040, 2, 4, 0, 0), datetime.datetime(2040, 2, 5, 0, 0), datetime.datetime(2040, 2, 6, 0, 0)]

On my little laptop that is nearly instant.