deep copy in python

Question

I was working with Python deep copy trying to create a total copy of original object, but the deep copy didn't seem to create a copy. It still shares the same reference with original object, which is not desired

Here's the code. I have a class Board, the instance of which I want to deep copy.

import copy
class Board:
    xpos = None
    opos = None
    count = None
    status = []

    def __init__(self, size):
        self.xpos=[0,0]
        self.opos=[size-1,size-1]
        self.count = size*size-2
        for i in range(size):
            tmp = ['-']*size
            self.status.append(tmp)
        self.status[0][0] = 'X'
        self.status[size-1][size-1]= 'O'

Somewhere in another function I want to call

board=Board()
localboard=copy.deepcopy(board)
# then do modification to local board....
# but it seems the old board is also affected. This is so weird since
# I am already using deep copy.

So how can I create a deep copy of the old board? I don't want to share any reference, since I will do modification on the local one and want to keep the old intact..

This has nothing to do with deepcopy and everything with the mutable class attribute you gave your class. — Martijn Pieters, Mar 23 '13 at 15:51

score 1 · Accepted Answer · answered Mar 23 '13 at 15:52

1

You should remove the following from the Board definition:

xpos = None
opos = None
count = None
status = []

and add the following to its __init__():

self.status = []

Otherwise all your instances share the same status, which is an attribute of the class, not of the instance.

answered Mar 23 '13 at 15:52

NPE

486,780
108
951
1,012

Big thanks, I think it's the my fault of messing up with instance variable and class variable – Daniel Mar 23 '13 at 16:00

deep copy in python

1 Answers1