How to properly implement helper functions in a class in python-CodePudding

I am fairly new to python, and I am trying to design a class to solve the N Queen Problem. This is my class def:

class QueenSolver:

    def genEmptyBoard(self, n):
        # Generates an empty board of n width and n height
        board = []
        for _ in range(n):
            board.append([0 for _ in range(n)])
        return board

    def genLegalBoard(self, q1, q2, n):
        # Returns legal board or false
        board = self.genEmptyBoard(self, n)
        try:
            board[q1[0]][q1[1]] = 'q'
        except IndexError:
            print("Queen placed outside of board constraints")
            return False
        try:
            if board[q2[0]][q2[1]] == 'q':
                print("Queens cannot be placed in the same position")
                return False
            board[q2[0]][q2[1]] = 'Q'
        except IndexError:
            print("Queen placed outside of board constraints")
            return False 
        return board

However, when I call this method outside of the class, like this:

board = QueenSolver.genLegalBoard([0, 0], [7, 7], 8)

I get an error that looks like this:

Exception has occurred: TypeError
QueenSolver.genLegalBoard() missing 1 required positional argument: 'n'

Apparently I have to supply the "self" variable when calling it from outside the class definition? I thought the "self" parameter doesn't require any value, because it is assumed? What am I missing here?

CodePudding user response：

You need to Instantiate an object of QueenSolver class before calling the method of the class. As well as, remove self from board = self.genEmptyBoard(self, n).

class QueenSolver:

    def genEmptyBoard(self, n):
        # Generates an empty board of n width and n height
        board = []
        for _ in range(n):
            board.append([0 for _ in range(n)])
        return board

    def genLegalBoard(self, q1, q2, n):
        # Returns legal board or false
        board = self.genEmptyBoard(n)
        try:
            board[q1[0]][q1[1]] = 'q'
        except IndexError:
            print("Queen placed outside of board constraints")
            return False
        try:
            if board[q2[0]][q2[1]] == 'q':
                print("Queens cannot be placed in the same position")
                return False
            board[q2[0]][q2[1]] = 'Q'
        except IndexError:
            print("Queen placed outside of board constraints")
            return False 
        return board

QS = QueenSolver()
board = QS.genLegalBoard([0, 0], [7, 7], 8)

Output:

[['q', 0, 0, 0, 0, 0, 0, 0],
 [0, 0, 0, 0, 0, 0, 0, 0],
 [0, 0, 0, 0, 0, 0, 0, 0],
 [0, 0, 0, 0, 0, 0, 0, 0],
 [0, 0, 0, 0, 0, 0, 0, 0],
 [0, 0, 0, 0, 0, 0, 0, 0],
 [0, 0, 0, 0, 0, 0, 0, 0],
 [0, 0, 0, 0, 0, 0, 0, 'Q']]