# 1. built-in sum() function
original_list = [[11, 22, 33, 44], [55, 66, 77], [88, 99]]
flatList = sum(original_list, [])
# output: [11, 22, 33, 44, 55, 66, 77, 88, 99]
# don't forget to upvote :)
# 2. List comprehension
original_list = [[11, 22, 33, 44], [55, 66, 77], [88, 99, 100]]
flatList = [element for innerList in original_list for element in innerList]
# output: [11, 22, 33, 44, 55, 66, 77, 88, 99, 100]
# 3. numpy
import numpy as np
original_list = [[11, 33], [22, 55], [11], [77, 88]]
flatList = list(np.concatenate(original_list))
# output: [11, 33, 22, 55, 11, 77, 88]