Creating 2D array without Numpy

[ichabod801]

The first way doesn't work because [[0] * n] creates a mutable list of zeros once. Then when the second *n copies the list, it copies references to first list, not the list itself. So you have a list of references, not a list of lists.

The second way a new [0] * n is created each time through the loop. That way there is no copying being done, so you end up with an actual list of lists. I often do the second way with a list comprehension:

[[0] * n for row in n]