CODEWITHSUNDEEP
python
Jon Hrovat
Jon Hrovat

Reputation: 595

Python: storing object in 2d array and calling its method

I'm trying my hand at making a chess app. Code below:

#file containing pieces classes
class Piece(object):`

     name = "piece"
     value = 0
     grid_name = "____"


class Pawn(Piece):

# Rules for pawns.
#If first move, then can move forward two spaces

name = "Pawn"
value = 1
grid_name = "_PN_"
first_move = True


#Main file
from Piece import *



class GameBoard:

   pieces = []
   grid = [][]

   def __init__(self):

      self.grid[1][0] = self.pieces.append(Pawn())



currentBoard = GameBoard()

I want to call the value variable for the object located at grid[1][0]

It would look something like:

 print currentBoard.grid[1][0].value

This code doesn't work which tells me I'm missing something regarding the scope of the objects and variables. Is this something that is possible in Python?

EDIT - Solution

I did find a solution to this in using the grid list to hold a reference to the indexing of the objects in the pieces list. Code below:

class GameBoard:

    # initialize empty board
    grid = [["____" for i in range(8)] for j in range(8)]
    pieces = []

    def __init__(self):

        self.grid[0][0] = 0
        self.grid[0][1] = 1
        self.grid[0][2] = 2
        self.grid[0][3] = 3
        self.grid[0][4] = 4
        self.grid[0][5] = 5
        self.grid[0][6] = 6
        self.grid[0][7] = 7
        self.grid[1][0] = 8
        self.grid[1][1] = 9
        self.grid[1][2] = 10
        self.grid[1][3] = 11
        self.grid[1][4] = 12
        self.grid[1][5] = 13
        self.grid[1][6] = 14
        self.grid[1][7] = 15


pieces = []

pieces.append(Pawn())

#grid will return the integer which can be passed to the other list to pull an 
#object for using the .value attribute

print pieces[currentBoard.grid[1][0]].value

Upvotes: 1

Views: 1943

Answers (1)

Mark Hannel
Mark Hannel

Reputation: 795

Rewriting your code so that it simply runs as a single file:

#file containing pieces classes
class Piece(object):
     name = "piece"
     value = 0
     grid_name = "____"


class Pawn(Piece):
    # Rules for pawns.
    #If first move, then can move forward two spaces

    name = "Pawn"
    value = 1
    grid_name = "_PN_"
    first_move = True

class GameBoard:

   pieces = []
   grid = [[],[]]

   def __init__(self):

      self.grid[0][1] = self.pieces.append(Pawn())



currentBoard = GameBoard()

There are a few things that need to be corrected. For one, the variables defined in Piece, Pawn and GameBoard are not defined under the __init__() method. This means that these variables will be shared by all instances of the class.

Example:

>>> pawn1 = Pawn()  # Make two Pawns
>>> pawn2 = Pawn()
>>> print pawn1.first_move, pawn2.first_move
True, True
>>> pawn1.first_move = False  # Change the first pawns attribute
>>> print pawn1.first_move, pawn2.first_move # But both change
False, False

To avoid this, define your class attributes under the method __init__() for all three of your classes.

Example:

class Pawn(Piece):
    # Rules for pawns.
    #If first move, then can move forward two spaces
    def __init__(self):
        self.name = "Pawn"
        self.value = 1
        self.grid_name = "_PN_"
        self.first_move = True

Next, your variable grid is not properly defined in python. If you wanted a list with two empty lists you could do the following

grid = [[], []]

But an easy way to make an 8x8 structure of empty lists would be to do the following

grid = [[[] for i in xrange(8)] for j in xrange(8)]

Upvotes: 1

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