copy.deepcopy() caused the input value repeated in all the list of the list group, Python

Asked May 29 '17 at 00:06

Active May 29 '17 at 00:06

Viewed 23 times

n = 4 
chessboard_lines_initial = [[0]*n]*n
chessboard_lines = copy.deepcopy(chessboard_lines_initial)
print(chessboard_lines)
#Output: 
#[[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]]

chessboard_lines[2][2] = 1
print(chessboard_lines)
#Output: 
#[[0, 0, 1, 0], [0, 0, 1, 0], [0, 0, 1, 0], [0, 0, 1, 0]]
#However, I was expecting 
#[[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 1, 0], [0, 0, 0, 0]]

however, if I directly assign [[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]] to chessboard_lines, then it works.

Not sure why the copy.deepcopy(chessboard_lines_initial) is not working in this case.

asked May 29 '17 at 00:06

New to Python and Django

The deep copy copies the already-wrong structure of `chessboard_lines_initial`. – user2357112 May 29 '17 at 00:16
When you do `[[0]*n]*n` all the list you are creating are the same. You are just creating 4 references to the same list. – Christian Dean May 29 '17 at 00:17
The duplicate doesn't address why deepcopy works this way. Deepcopy attempts to preserve relationships of shared data in the source into the copy, so you get the same shared structure in the copy – John La Rooy May 29 '17 at 00:23
Thanks! everyone, I was not aware that it was the "[[0]*n]*n" caused the issue!!!! Thanks for pointing that out! – New to Python and Django May 29 '17 at 04:47

copy.deepcopy() caused the input value repeated in all the list of the list group, Python

0 Answers0