[Python] Fast way to expand split list into index list

Given an index split list T of length M + 1, where the first element is 0 and the last element is N, generate an array D of length N such that D[T:T[i+1]] = i.

For example, given T = [0, 2, 5, 7], then return D = [0, 0, 1, 1, 1, 2, 2].

I'm trying to avoid a for loop, but the best I can do is:

def expand_split_list(split_list):
return np.concatenate(
[
np.full(split_list[i + 1] - split_list, i)
for i in range(len(split_list) - 1)
]
)


Is there a built-in function for that purpose?

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