如何从 Python 3 中的字典键定义可能的 input() 变量？

Question

I am just starting out and creating a TicTacToe game in Python 3 using a dictionary instead of a list.

The possibles moves for the game are the same as the number grid on a keyboard (1-9), which are defined by a dictionary.

I'm happy with how the game runs, except if I input a value that is not between 1-9, it will produce an error.

How do I define it so that if a value that is != 1-9 , instead of an error it will print('Sorry, that value is not valid.\nPlease select a value between 1-9.\n') and give the user an opportunity to try again?

Below is a snippet of my code:

# Creating the board using dictionary, using numbers from a keyboard

game_board = {'7': ' ', '8': ' ', '9': ' ',
              '4': ' ', '5': ' ', '6': ' ',
              '1': ' ', '2': ' ', '3': ' '}

board_keys = []

for key in game_board:
    board_keys.append(key)

# Print updated board after every move

def print_board(board):
    print(board['7'] + '|' + board['8'] + '|' + board['9'])
    print('-+-+-')
    print(board['4'] + '|' + board['5'] + '|' + board['6'])
    print('-+-+-')
    print(board['1'] + '|' + board['2'] + '|' + board['3'])

# Gameplay functions

def game():

    turn = 'X'
    count = 0

    for i in range(10):
        print_board(game_board)
        print("\nIt's " + turn + "'s turn. Pick a move.\n")

        move = input()

        if game_board[move] == ' ':
            game_board[move] = turn
            count += 1

        else:
            print('Sorry, that position has already been filled.\nPlease pick another move.\n')
            continue

Thankyou in advance.

Answer 1

You have this code:

 game_board = {'7': ' ', '8': ' ', '9': ' ', '4': ' ', '5': ' ', '6': ' ', '1': ' ', '2': ' ', '3': ' '} #... move = input() if game_board[move] == ' ': game_board[move] = turn count += 1 else: print('Sorry, that position has already been filled.\nPlease pick another move.\n') continue

If the users enters anything else than a digit between 1 and 9 this will already create a KeyError because the lookup game_board[move] will fail.

So all you have to do is handle the KeyError and create the desired error message:

move = input()

try:
    current_value = game_board[move]
except KeyError:
    print('Sorry, that value is not valid.\nPlease select a value between 1-9.\n')
    continue

if current_value == ' ':
    game_board[move] = turn
    count += 1
else:
    print('Sorry, that position has already been filled.\nPlease pick another move.\n')
    continue

Answer 2

This is a good use case for a while loop. move could be invalid every time the user enters their move. Plus we need to make sure the user's input is a valid number and constrained to the correct range.

"While move is not valid, try again."

def getMoveForPlayer(playerName: str) -> int:
  move = -1 # Default invalid value so the loop runs
  moveHasBeenEntered = False

  print(f"It's {playerName}'s turn. Pick a move: ", end="")

  while move < 1 or move > 9:
    if moveHasBeenEntered:
      print('Sorry, that value is not valid.\nPlease select a value between 1-9: ', end="")
    else:
      moveHasBeenEntered = True

    try:
      move = int(input())
    except ValueError:
      pass

  return move

# This line replaces "move = input()"
move = getMoveForPlayer("Sky")

Note that the value returned from getMoveForPlayer is an integer. If you need it to be a string, then cast the returned value to a string:

move = str(getMoveForPlayer("Sky"))