Move everything to Board class; implement format()

tictactoe.py

@@ -1,23 +1,40 @@
 from flask import Flask, abort, request
 
+BOARD_SIZE = 9
+
 app = Flask(__name__)
 
+class Board:
+    Empty = ' '
+    X = 'x'
+    O = 'o'
+
+    def __init__(self, string):
+        if string is None or not isinstance(string, str):
+            raise ValueError('invalid board spec')
+        if len(string) != BOARD_SIZE:
+            raise ValueError('board spec should be {} characters long'.format(BOARD_SIZE))
+
+        # Process the board into an array.
+        self.board = string.lower()
+
+    def format(self):
+        out = ''
+        board_len = len(self.board)
+        for x in range(board_len):
+            out += self.board[x]
+            x_mod = x % 3
+            if x_mod == 0 or x_mod == 1:
+                out += '|'
+            elif x_mod == 2 and x != (board_len - 1):
+                out += '\n-+-+-\n'
+        return out
+
 @app.route('/')
 def hello():
-    board = _get_board_or_abort()
-    return board
-
-def _get_board_or_abort():
-    '''
-    Get the board from the request, or abort the request with a 400 error.
-    '''
-    board = request.args.get('board', None)
-    is_valid = all(
-        board is not None,  # 'board' var must exist.
-        len(board) >= 9,    # Board should be at least 9 characters long.
-    )
-
-    if not is_valid:
+    try:
+        board = Board(request.args.get('board', None))
+    except ValueError:
         abort(400)
 
-    return board
+    return (board.format(), 200, {'Content-type': 'text/plain'})