N queen problem implementation in python

class NQueen:    def __init__(self, n):        self.n = n        self.board = self.create_borad(self.n)        self.queens = 0        self.row_exist = [0 for i in range(n)] # row check queen exist        self.col_exist = [0 for i in range(n)] # column check queen exist        self.main_exist = [0 for i in range(2 * n - 1)] # main diagnosis check queen exist        self.vice_exist = [0 for i in range(2 * n - 1)] # vice diagnosis check queen exist                self.count = 0 # number of solution            # create the n queen board    def create_borad(self, n):        board = [[0 for row in range(n)] for col in range(n)]        return board        # return the size of the board    def size(self):        return self.n        # return the number of queens on the board    def num_queens(self):        return self.queens        # check if the cell can put a queen    def unguarded(self, row, col):        if self.row_exist[row] == 1:            return False        if self.col_exist[col] == 1:            return False        if self.main_exist[self.n + row - col - 1] == 1:            return False        if self.vice_exist[row + col] == 1:            return False                return True        # place a queen on the board    def place_queen(self, row, col):        self.board[row][col] = 1        self.queens += 1        self.row_exist[row] = 1        self.col_exist[col] = 1        self.main_exist[self.n + row - col - 1] = 1        self.vice_exist[row + col] = 1        # remove a queen from the board    def remove_queen(self, row, col):        self.board[row][col] = 0        self.queens -= 1        self.row_exist[row] = 0        self.col_exist[col] = 0        self.main_exist[self.n + row - col - 1] = 0        self.vice_exist[row + col] = 0        # draw the queens board    def draw(self):        for i in range(self.size()):            print self.board[i]#            for j in range(self.size()):#                print self.board[i][j]#            print        # backtracking solve the problem    def solve(self, row, col):        if row > self.n:            return         if self.num_queens() == self.n:            self.count += 1            print 'the count is: ', self.count            self.draw()        else:            for row in range(self.size()):                if self.unguarded(row, col):                    self.place_queen(row, col)                    self.solve(row + 1, col + 1)                    self.remove_queen(row, col)if __name__ == '__main__':    q = NQueen(8)    q.solve(0, 0)