Automate the Boring Stuff – Chapter 5 – Chess Dictionary Validator [closed]

First post, new to programming and having fun! All feedback on this post and my questions are welcome.

I’m working through Automate the Boring Stuff and attacking the first Chapter 5 problem Chess Dictionary Validator.

In this chapter, we used the dictionary value {‘1h’: ‘bking’, ‘6c’: ‘wqueen’, ‘2g’: ‘bbishop’, ‘5h’: ‘bqueen’, ‘3e’: ‘wking’} to represent a chess board. Write a function named isValidChessBoard() that takes a dictionary argument and returns True or False depending on if the board is valid.

A valid board will have exactly one black king and exactly one white king. Each player can only have at most 16 pieces, at most 8 pawns, and all pieces must be on a valid space from ‘1a’ to ‘8h’; that is, a piece can’t be on space ‘9z’. The piece names begin with either a ‘w’ or ‘b’ to represent white or black, followed by ‘pawn’, ‘knight’, ‘bishop’, ‘rook’, ‘queen’, or ‘king’. This function should detect when a bug has resulted in an improper chess board.

my questions and code:

1. Is evaluating dictionary keys/values through these for loops + multiple if statements the “best practice”? It seems like a lot of code. Changing to include some elif caused issues if it followed with another if statement in the for loop.
2. Line 23 if i[0] == 'b': errors out because the chess spaces which are empty string values have no character at i[0]. What’s the best way to express/evaluate empty values? If it is with ”, should I add leading condition in the loop which evaluates value == ”, and then ‘continue’?
3. Why can I not collapse line 15 into 11 such that I have one statement: if 'bking' or 'wking' not in board.values():? If I try that, the statement result is True; however the dictionary contains both values so shouldn’t it evaluate to False and keep the code running?

def isValidChessBoard(board):
    while True:
        blackPieces = 0
        whitePieces = 0
        wpawn = 0
        bpawn = 0
        letterAxis = ('a','b','c','d','e','f','g','h')
        pieceColour = ('b','w')
        pieceType = ('pawn','knight','bishop','rook','queen','king')

        #one black king and one white king
        if 'bking' not in board.values():
            print('KingError')
            return False
            break
        if 'wking' not in board.values():
            print('KingError')
            return False
            break

        #each player has <= 16 pieces
        for i in board.values():
            if i[0] == 'b':
                blackPieces+=1
            if i[0] == 'w':
                whitePieces+=1
            if whitePieces >= 17:
                print('TotalPieceError')
                return False
                break
            if blackPieces >= 17:
                print('TotalPieceError')
                return False
                break

        #each player has <= 8 pawns
        for i in board.values():
            if i == 'wpawn':
                wpawn+=1
            elif i == 'bpawn':
                bpawn+=1
            if wpawn or bpawn >= 9:
                print('PawnError')
                return False
                break

        #all pieces must be on valid space from '1a' to '8h'
        for i in board.keys():
            if int(i[0]) >= 9:
                print('SpacesError')
                return False
                break
            if i[1] not in letterAxis:
                print('yAxisError')
                return False
                break

        #piece names begin with 'w' or 'b'
        for i in board.values():
            if i[0] not in pieceColour:
                print('WhiteOrBlackError')
                return False
                break

        #piece names must follow with 'pawn', 'knight', 'bishop', 'rook', 'queen', 'king'
        for i in board.values():
            if i[1:] not in pieceType:
                print('PieceTypeError')
                return False
        return 'This board checks out'

board = {'1a': 'bking','2a': 'bqueen','3a': 'brook','4a': 'brook',
'5a': 'bknight','6a': 'bknight','7a':'bbishop','8a': 'bbishop',
'1b': 'bpawn','2b': 'bpawn','3b': 'bpawn','4b':'bpawn',
'5b': 'bpawn','6b': 'bpawn','7b': 'bpawn','8b': 'bpawn',
'1c': 'wking','2c': 'wqueen','3c': 'wrook','4c': 'wrook',
'5c': 'wbishop','6c': 'wbishop','7c': 'wknight','8c':'wknight',
'1e': 'wpawn','2e': 'wpawn','3e': 'wpawn','4e': 'wpawn',
'5e': 'wpawn','6e': 'wpawn','7e': 'wpawn','8e': 'wpawn',
'1f': '','2f': '','3f': '','4f': '','5f': '','6f': '','7f': '','8f': '',
'1g': '','2g': '','3g': '','4g': '','5g': '','6g': '','7g': '','8g': '',
'1h': '','2h': '','3h': '','4h': '','5h': '','6h': '','7h': '','8h': '',}

print(isValidChessBoard(board))

Error:
Traceback (most recent call last):
line 23, in isValidChessBoard
    if i[0] == 'b':
IndexError: string index out of range

Answer

Edit: When you define valid count, it doesn’t take into consideration that you might get a pawn to the other end of the board and end up with two queens, though I don’t know how you could fix this without causing the program to accept wonky answers (such as two queens at the start of a game for instance). Any help here would be appreciated!

Since you asked if there was an alternative I present the following.

Steps

• Define the set of all chess pieces
• Define the valid count range of pieces by type
• Count the pieces on the board
• Check pieces counts in a valid range
• Check that positions are valid
• Check that pieces names are valid

Code

def isValidChessBoard(board):
      """Validate counts and location of pieces on board"""
    
      # Define pieces and colors
      pieces = ['king','queen','rook', 'knight','bishop', 'pawn']
      colors = ['b', 'w']
      # Set of all chess pieces
      all_pieces = set(color+piece for piece in pieces for color in colors)
    
      # Define valid range for count of chess pieces by type (low, high) tuples
      valid_counts = {'king': (1, 1),
                  'queen': (0, 1),
                  'rook': (0, 2),
                  'bishop': (0, 2),
                  'knight': (0, 2),
                  'pawn': (0, 8)}
    
      # Get count of pieces on the board
      piece_cnt = {}
      for v in board.values():
        if v in all_pieces:
          piece_cnt.setdefault(v, 0)
          piece_cnt[v] += 1
    
      # Check if there are a valid number of pieces
      for piece in all_pieces:
        cnt = piece_cnt.get(piece, 0)
        lo, hi = valid_counts[piece[1:]]
        if not lo <= cnt <= hi:   # Count needs to be between lo and hi
          if lo != hi:
            print(f"There should between {lo} and {hi} {piece} but there are {cnt}")
          else:
            print(f"There should be {lo} {piece} but there are {cnt})")
          return False
    
      # Check if locations are valid
      for location in board.keys():
        row = int(location[:1])
        column = location[1:]
        if not ((1 <= row <= 8) and ('a' <= column <= "h")):
          print(f"Invaid to have {board[location]} at postion {location}")
          return False

      # Check if all pieces have valid names
      for loc, piece in board.items():
        if piece:
          if not piece in all_pieces:
            print(f"{piece} is not a valid chess piece at postion {loc}")
            return False

      return True