Pyupgrade to Python 3.9 (#4718)

* Pyupgrade to Python 3.9

* updating DIRECTORY.md

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>

machine_learning/similarity_search.py

@@ -7,8 +7,9 @@ returns a list containing two data for each vector:
     1. the nearest vector
     2. distance between the vector and the nearest vector (float)
 """
+from __future__ import annotations
+
 import math
-from typing import List, Union
 
 import numpy as np
 
@@ -33,7 +34,7 @@ def euclidean(input_a: np.ndarray, input_b: np.ndarray) -> float:
 
 def similarity_search(
     dataset: np.ndarray, value_array: np.ndarray
-) -> List[List[Union[List[float], float]]]:
+) -> list[list[list[float] | float]]:
     """
     :param dataset: Set containing the vectors. Should be ndarray.
     :param value_array: vector/vectors we want to know the nearest vector from dataset.