**This tutorial is part of a series. Make sure to check out the previous tutorial, if you haven't already.**

In this tutorial, we will add a functionality to the Tic-Tac-Toe game: **Player vs Computer** 👀

## Logic in Tic-Tac-Toe 🎮

Let's go ahead and create a function for the computer to determine the moves in this game.

```
def auto_play():
```

Before completing the code, let's take a look at the logic 🤔:

### 1. When the game can be won on the next move, either by the computer or the player

When the game can be won on the next move by computer, the move should be done. If the game can be won by player on the next move, the best option is to prevent it. It can be implemented in Python as:

```
# If winning of computer is possible on the next move, go ahead and win the game
for winning_possibility in winning_possibilities:
winning_possibility.check('O') # Check how many conditions for winning of computer are satisfied
if winning_possibility.p1_satisfied and winning_possibility.p2_satisfied: # If condition 1 and 2 are satisfied, satisfy condition 3
for point in XO_points:
if point.x == winning_possibility.x3 and point.y == winning_possibility.y3 and point not in X_points + O_points: # Find the point that needs to be occupied to satisfy condtion 3 and make sure that it is not already occupied
point.set() # Occupy point
return # End the function
elif winning_possibility.p2_satisfied and winning_possibility.p3_satisfied: # If condition 2 and 3 are satisfied, satisfy condition 1
for point in XO_points:
if point.x == winning_possibility.x1 and point.y == winning_possibility.y1 and point not in X_points + O_points: # Find the point that needs to be occupied to satisfy condition 1 and make sure that it is not already occupied
point.set() # Occupy point
return # End the function
elif winning_possibility.p3_satisfied and winning_possibility.p1_satisfied: # If condition 1 and 3 are satisfied, satisfy condition 2
for point in XO_points:
if point.x == winning_possibility.x2 and point.y == winning_possibility.y2 and point not in X_points + O_points: # Find the point that needs to be occupied to satisfy condition 2 and make sure that it is not already occupied
point.set() # Occupy point
return # End the function
# If the player might win on the next move, prevent it
for winning_possibility in winning_possibilities:
winning_possibility.check('X') # Check how many conditions for winning of player are satisfied
if winning_possibility.p1_satisfied and winning_possibility.p2_satisfied: # If condition 1 and 2 are satisfied, prevent condition 3 from being satisfied
for point in XO_points:
if point.x == winning_possibility.x3 and point.y == winning_possibility.y3 and point not in X_points + O_points: # Find the point and make sure that it is not already occupied
point.set() # Occupy point
return # End function
elif winning_possibility.p2_satisfied and winning_possibility.p3_satisfied: # If condition 2 and 3 are satisfied, prevent condition 1 from being satisfied
for point in XO_points:
if point.x == winning_possibility.x1 and point.y == winning_possibility.y1 and point not in X_points + O_points: # Find the point and make sure that it is not already occupied
point.set() # Occupy point
return # End function
elif winning_possibility.p3_satisfied and winning_possibility.p1_satisfied: # If condition 1 and 3 are satisfied, prevent condition 2 from being satisfied
for point in XO_points:
if point.x == winning_possibility.x2 and point.y == winning_possibility.y2 and point not in X_points + O_points: # Find the point and make sure that it is not already occupied
point.set() # Occupy point
return # End function
```

#### Some changes to function "check" in class "WinningPossibility"

To check how many conditions are currently satisfied to win the game, we need to make variables `p1_satisfied`

, `p2_satisfied`

and `p3_satisfied`

accessible outside the function. So, let's rename them as `self.p1_satisfied`

, `self.p2_satisfied`

and `self.p3_satisfied`

respectively. The new code for the function would be:

```
def check(self, for_chr):
self.p1_satisfied = False
self.p2_satisfied = False
self.p3_satisfied = False
if for_chr == 'X':
for point in X_points:
if point.x == self.x1 and point.y == self.y1:
self.p1_satisfied = True
elif point.x == self.x2 and point.y == self.y2:
self.p2_satisfied = True
elif point.x == self.x3 and point.y == self.y3:
self.p3_satisfied = True
elif for_chr == 'O':
for point in O_points:
if point.x == self.x1 and point.y == self.y1:
self.p1_satisfied = True
elif point.x == self.x2 and point.y == self.y2:
self.p2_satisfied = True
elif point.x == self.x3 and point.y == self.y3:
self.p3_satisfied = True
return all([self.p1_satisfied, self.p2_satisfied, self.p3_satisfied])
```

### 2. If center is not currently occupied

It's a good idea to occupy the center if it's not currently occupied. It can be implemented in Python as:

```
center_occupied = False
for point in X_points + O_points: # Check if center is already occupied
if point.x == 2 and point.y == 2:
center_occupied = True
break
if not center_occupied: # If center is not occupied
for point in XO_points:
if point.x == 2 and point.y == 2:
point.set() # Occupy center
return # End the function
```

### 3. If the center is already occupied, and currently there is no winning possibility

In this case, we need to occupy either a corner point or a middle one. If fewer than two corners are occupied by the player, "O" must try to occupy the rest. If 2 or more corners are occupied by the player, it is safer to occupy the middle points instead. This can be implemented in Python as:

```
corner_points = [(1, 1), (1, 3), (3, 1), (3, 3)]
middle_points = [(1, 2), (2, 1), (2, 3), (3, 2)]
num_of_corner_points_occupied_by_X = 0
for point in X_points: # Iterate over all points occupied by the player
if (point.x, point.y) in corner_points:
num_of_corner_points_occupied_by_X += 1
if num_of_corner_points_occupied_by_X >= 2: # If two or more corner points are occupied by the player
for point in XO_points:
if (point.x, point.y) in middle_points and point not in X_points + O_points: # Find a middle point and make sure that it is not already occupied
point.set() # Occupy the point
return # End the function
elif num_of_corner_points_occupied_by_X < 2: # If less than two corner points are occupied by the player
for point in XO_points:
if (point.x, point.y) in corner_points and point not in X_points + O_points: # Find a corner point and make sure that it is not already occupied
point.set() # Occupy the point
return # End the function
```

###
Combining all code, let's write the function `auto_play`

:

```
def auto_play():
# If winning is possible in the next move
for winning_possibility in winning_possibilities:
winning_possibility.check('O')
if winning_possibility.p1_satisfied and winning_possibility.p2_satisfied:
for point in XO_points:
if point.x == winning_possibility.x3 and point.y == winning_possibility.y3 and point not in X_points + O_points:
point.set()
return
elif winning_possibility.p2_satisfied and winning_possibility.p3_satisfied:
for point in XO_points:
if point.x == winning_possibility.x1 and point.y == winning_possibility.y1 and point not in X_points + O_points:
point.set()
return
elif winning_possibility.p3_satisfied and winning_possibility.p1_satisfied:
for point in XO_points:
if point.x == winning_possibility.x2 and point.y == winning_possibility.y2 and point not in X_points + O_points:
point.set()
return
# If the opponent can win in the next move
for winning_possibility in winning_possibilities:
winning_possibility.check('X')
if winning_possibility.p1_satisfied and winning_possibility.p2_satisfied:
for point in XO_points:
if point.x == winning_possibility.x3 and point.y == winning_possibility.y3 and point not in X_points + O_points:
point.set()
return
elif winning_possibility.p2_satisfied and winning_possibility.p3_satisfied:
for point in XO_points:
if point.x == winning_possibility.x1 and point.y == winning_possibility.y1 and point not in X_points + O_points:
point.set()
return
elif winning_possibility.p3_satisfied and winning_possibility.p1_satisfied:
for point in XO_points:
if point.x == winning_possibility.x2 and point.y == winning_possibility.y2 and point not in X_points + O_points:
point.set()
return
# If the center is free...
center_occupied = False
for point in X_points + O_points:
if point.x == 2 and point.y == 2:
center_occupied = True
break
if not center_occupied:
for point in XO_points:
if point.x == 2 and point.y == 2:
point.set()
return
# Occupy corner or middle based on what opponent occupies
corner_points = [(1, 1), (1, 3), (3, 1), (3, 3)]
middle_points = [(1, 2), (2, 1), (2, 3), (3, 2)]
num_of_corner_points_occupied_by_X = 0
for point in X_points:
if (point.x, point.y) in corner_points:
num_of_corner_points_occupied_by_X += 1
if num_of_corner_points_occupied_by_X >= 2:
for point in XO_points:
if (point.x, point.y) in middle_points and point not in X_points + O_points:
point.set()
return
elif num_of_corner_points_occupied_by_X < 2:
for point in XO_points:
if (point.x, point.y) in corner_points and point not in X_points + O_points:
point.set()
return
```

## Creating a button to toggle play with a computer or play with a human

Let’s create a button that can switch opponents as either human or computer, as well as make a callback to change the toggle button text and command.

```
play_with = "Computer"
def play_with_human():
global play_with
play_with = "Human" # switch opponent to human
play_with_button['text'] = "Play with computer" # switch text
play_with_button['command'] = play_with_computer # switch command so that the user can play with the computer again, if required
play_again() # restart game
def play_with_computer():
global play_with
play_with = "Computer" # switch opponent to computer
play_with_button['text'] = "Play with human" # switch text
play_with_button['command'] = play_with_human # switch command so that the user can play with a human again, if required
play_again() # restart game
play_with_button = tk.Button(root, text='Play with human', font=('Ariel', 15), command=play_with_human)
play_with_button.pack()
```

We need to call the function `auto_play`

whenever it's O's turn and the value of `play_with`

is `"Computer"`

. For this, append the following code to the function `set`

in class `XOPoint`

:

```
if play_with == "Computer" and status_label['text'] == "O's turn":
auto_play()
```

## Result

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Full code in GitHub repository: https://github.com/Jothin-kumar/tic-tac-toe/

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