Tic-Tac-Toe (Python CLI)

A compact two-player console game

Overview

This was a group assignment to implement a two-player Tic-Tac-Toe game in Python. The program renders a 3×3 board, alternates turns between Player 1 (X) and Player 2 (O), validates moves with a regular expression, prevents overwriting occupied squares, and reports win or tie outcomes. The board is stored as a 10-element list so positions 1 through 9 map directly to the grid for simple input.


Key Features

  • Clear console UI A simple ASCII board, explicit prompts, and immediate redraw after each move.
  • Strict input validation A compiled regex ^[1-9]$ ensures users enter digits 1 to 9 only. Illegal or occupied choices trigger a helpful message and a re-prompt.
  • Deterministic win detection A single win(panels, sign) check tests all rows, columns, and diagonals for either X or O.
  • Accurate end states The game declares a winner as soon as a line is formed. If nine moves complete without a line, a tie is reported.


How It Works

Board model

  • panels is a 10-slot list, index 0 unused, indices 1–9 map to the grid:

    1 | 2 | 3
4 | 5 | 6
7 | 8 | 9

  • PrintGameBoard() renders the current state with X, O, or space.

Turn loop

  • count starts at 0 and increments after each valid move.
  • Even count selects Player 1 (X). Odd count selects Player 2 (O).
  • IsDigit() reads the user choice, validates via regex, then defers to CheckEmpty() to ensure the square is free.

Win and tie

  • win(panels, sign) returns true if any of the eight three-in-a-row patterns match the given sign.
  • isGameFinished(sign) prints the winner and exits, or reports a tie when nine moves have been placed.


Refinements I Would Apply

These are drop-in improvements that keep the visible behavior the same while tightening correctness and readability.

  1. Centralize winning lines Replace chained comparisons with a tuple list for clarity.

    WINS = [(1,2,3),(4,5,6),(7,8,9),(1,4,7),(2,5,8),(3,6,9),(1,5,9),(3,5,7)]
def win(panels, s):
    return any(panels[a]==panels[b]==panels[c]==s for a,b,c in WINS)

  2. Looped input instead of recursion Convert IsDigit() and CheckEmpty() to a single loop that continues until a valid empty square is returned. This avoids deep recursion on repeated bad input.


How to Run

python3 tictactoe.py

Use digits 1–9 to place your mark. The program enforces valid, empty squares and announces the result.