やりたいこと

以下のような変換を行う。

変換前

[
    [[1, 2], [3, 4], [5, 6]],
    [[7, 8], [9, 10]],
    [[11, 12]],
]

変換後

[[1, 2], [3, 4], [5, 6], [7, 8], [9, 10], [11, 12]]

リスト内包表記

flattened_list = [item for sublist in nested_list for item in sublist]

from itertools import chain
flattened_list = list(chain.from_iterable(nested_list))

flattened_list = sum(nested_list, [])

リストの加算で ['a', 'b'] + ['c'] が ['a', 'b', 'c'] になることをイメージするとわかりやすい。

flattend_list = []
for sublist in nested_list:
    flattend_list.extend(sublist)