Learn Classes and Objects by Building a Sudoku Solver - Step 51

Python
1

Tell us what’s happening:

Why should i have return True in the outermost loop rather than the innermost loop

Your code so far

class Board:
    def __init__(self, board):
        self.board = board

    def __str__(self):
        upper_lines = f'\n╔═══{"╤═══"*2}{"╦═══"}{"╤═══"*2}{"╦═══"}{"╤═══"*2}╗\n'
        middle_lines = f'╟───{"┼───"*2}{"╫───"}{"┼───"*2}{"╫───"}{"┼───"*2}╢\n'
        lower_lines = f'╚═══{"╧═══"*2}{"╩═══"}{"╧═══"*2}{"╩═══"}{"╧═══"*2}╝\n'
        board_string = upper_lines
        for index, line in enumerate(self.board):
            row_list = []
            for square_no, part in enumerate([line[:3], line[3:6], line[6:]], start=1):
                row_square = '|'.join(str(item) for item in part)
                row_list.extend(row_square)
                if square_no != 3:
                    row_list.append('║')

            row = f'║ {" ".join(row_list)} ║\n'
            row_empty = row.replace('0', ' ')
            board_string += row_empty

            if index < 8:
                if index % 3 == 2:
                    board_string += f'╠═══{"╪═══"*2}{"╬═══"}{"╪═══"*2}{"╬═══"}{"╪═══"*2}╣\n'
                else:
                    board_string += middle_lines
            else:
                board_string += lower_lines

        return board_string

    def find_empty_cell(self):
        for row, contents in enumerate(self.board):
            try:
                col = contents.index(0)
                return row, col
            except ValueError:
                pass
        return None

    def valid_in_row(self, row, num):
        return num not in self.board[row]

    def valid_in_col(self, col, num):
        return all(
            self.board[row][col] != num
            for row in range(9)
        )


# User Editable Region

    def valid_in_square(self, row, col, num):
        row_start = (row // 3) * 3
        col_start=(col // 3) * 3
        for row_no in range(row_start, row_start + 3):
            for col_no in range(col_start, col_start + 3):
                if self.board[row_no][col_no] == num:
                    return False
                    return True

# User Editable Region

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Challenge Information:

Learn Classes and Objects by Building a Sudoku Solver - Step 51

2

the first return met means the code stop executing
if you have two returns one after another like here:

only the first one will ever be executed, so this code is not going to work

logically, you want to return true when all the checks have been checked, because you can say it’s False with only one single check, but you need all the checks to say it’s true

3

Right, thanks for the clarification

4

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