Question

I have the following code

class Board:
    def __init__(self, size=7):
        self._size = size
        self._list, self._llist =[],[]
        for i in range (self._size):
            self._list.append('_ ')
        for j in range(self._size):
            self._llist.append(self._list)
    def printboard(self):
        for i in range(self._size):
            for j in range(self._size):
                print(self._llist[i][j], end = ' ')
            print('\n')

    def updateboard(self,x,y,letter):
        self._llist[x][y]=letter
        self.printboard()

board = Board(3)
board.updateboard(0,0,'c')

and this prints

c _  _ 

c _  _  

c _  _

instead of

c _  _ 

_ _  _  

_ _  _

I can’t see what is going wrong. Also, is there a simpler way to create the list of lists dynamically?

Thanks!

Answer 1

You are creating llist with the same list object, repeated multiple times. If you want each list in llist to be a separate, independent object (so that when you modify the contents only one list is changed) then you need to append a different copy to each. The easiest way to do this is to change:

self._llist.append(self._list)

to

self._llist.append(list(self._list))

Simpler code would be:

self._list = ['_ '] * self._size
self._llist = [list(self._list) for i in range(self._size)]