Add items in a list until their sum exceeds a threshold

Question

From a list of values I want to create a new list of values until they add up a value.

I am new with Python but I believe it is best done with a while loop.

L = [1,2,3,4,5,6,7,8,9]
i = 0
s = 0
while i < len(L) and s + L[i] < 20:
    s += L[i]
    i += 1

Answer 1

numpy arrays make this simple

import numpy as np

arr = np.array(L)
arr[arr.cumsum() <= 20].tolist()
#[1, 2, 3, 4, 5]

Answer 2

Since you tagged Pandas:

pd.Series(L, index=np.cumsum(L)).loc[:20].values

Output:

array([1, 2, 3, 4, 5], dtype=int64)