Как создать один список из 2D List Python
>>> l = [[1, 2, 3], [4, 5, 6], [7], [8, 9]]
>>> sum(l, [])
[1, 2, 3, 4, 5, 6, 7, 8, 9]
Obnoxious Oystercatcher
>>> l = [[1, 2, 3], [4, 5, 6], [7], [8, 9]]
>>> sum(l, [])
[1, 2, 3, 4, 5, 6, 7, 8, 9]length, breadth = x, y
matrix = [[-1 for j in range(breadth)] for i in range(length)]
# every element is -1