https://1coding.tistory.com/83

1. sum

a = [[60, 50], [30, 70], ['바보'], [60, 30], [80, 40]]
b = [[60], [30], [30], [40]]

>>> sum(a, [])
[60, 50, 30, 70, '바보', 60, 30, 80, 40]

>>>sum(b, [])
[60, 30, 30, 40]

2. list comprehension

b = [[60], [30], [30], [40]]

>>> [element for array in b for element in array]

3. numpy - flatten

import numpy as np 
b = [[1, 2], [3, 4], [5, 6]] 

>>> np.array(my_list).flatten().tolist()