Appending list to another list in range

Question

Hi,

I don't understand the output of this code:
L = []
D = []
for x in range (4):
D.append(x)
L.append(D)
print(L)
print(D)

I assumed that the output will be:
[[0], [0,1], [0,1,2], [0,1,2,3]]
[0,1,2,3]

The actual output is:
[[0, 1, 2, 3], [0, 1, 2, 3], [0, 1, 2, 3], [0, 1, 2, 3]]
[0, 1, 2, 3]

For me is clear that D = [0,1,2,3], but L is hard to understand.

Answer 1

D = something different at each iteration. 0, 01, 012, 0123.
L goes through iteration also.
0
01,01
012,012,012
0123,0123,0123,0123
After the final iteration that's what you have.

Answer 2

How should I change the code so that L = [[0], [0,1], [0,1,2], [0,1,2,3]]?

I still don't fully understand this. I thought that the function append adds an element only once but here it is addes 4 times at the final iteration?