A simplified Tic-Tac-Toe implementation in Python

Introduction

A simplified version of the TicTacToe game has been written in Python. This was done as part of a lab in the "PCAP - Programming Essentials In Python" course on Cisco Networking Academy (https://www.netacad.com/portal/learning).

The program showcases the use of:
    1. Tuples
    2. Dictionaries
    3. Two Dimensional Lists
    4. while Loop
    5. if statement
    6. functions

Assumption: The computer always starts with an X in the middle of the board.

Also, the board of the game is numbered from 1 to 9 with position 5 containing the X that represents the first move of the computer.  The initial state of the board will be as per Figure 1.

Figure 1: Initial state of the board.

Algorithm

Taking into consideration the above assumption, the steps to be executed are as follows:

    1. The board is displayed.

    2. User enters a number between 1 to 9 where the 'O' is to be placed.

    3. The updated board is displayed.

    4. If user has won or there is a tie, stop the game.

    5. The computer plays its move.

    6. The updated board is displayed.

    7.  If the computer has won or there is a tie, stop the game.

Note: Steps 2 to 7 are executed in an infinite loop until there is a winner or there is a tie.

Implementation

The board of the game is represented as a two dimensional list called "board".  It is a 3 by 3 array.

A dictionary, "dict_num_to_tup", is used to translate each position (1 to 9) in the board to its corresponding indices in the 2D array.

The following five functions have been defined:

    1. display_board(board)

            - It displays the current state of the board.

    2. enter_move(board)

            - It allows the user to enter a move.  Some basic validations have been included in the function.

    3. make_list_of_free_fields(board)

            - It determines and build a list of free cells in the board.  The list stores the indices of the free cells in the form of tuples.

    4. victory_for(board, sign)

            - It determines whether the "sign" passed as argument to the function has won the game or not.

    5. draw_move(board)

            - It allows the computer to play a move.  A random number generator function has been used to simulate the move of the computer.

Code

Below is the python code.  Same can also be executed by pressing the "play" button.