# Snake game in PyGTK

last modified July 16, 2020

In this part of the PyGTK programming tutorial, we will create a Snake game clone.

## Snake game

Snake is an older classic video game. It was first created in late 70s. Later it was brought to PCs. In this game the player controls a snake. The objective is to eat as many apples as possible. Each time the snake eats an apple, its body grows. The snake must avoid the walls and its own body. This game is sometimes called Nibbles.

## Development

The size of each of the joints of a snake is 10px. The snake is controlled with the cursor keys. Initially the snake has three joints. The game starts immediately. If the game is finished, we display "Game Over" message in the middle of the Board.

snake.py
```#!/usr/bin/python

# ZetCode PyGTK tutorial
#
# This is a simple snake game
# clone
#
# author: jan bodnar
# website: zetcode.com
# last edited: February 2009

import sys
import gtk
import cairo
import random
import glib

WIDTH = 300
HEIGHT = 270
DOT_SIZE = 10
ALL_DOTS = WIDTH * HEIGHT / (DOT_SIZE * DOT_SIZE)
RAND_POS = 26

x =  * ALL_DOTS
y =  * ALL_DOTS

class Board(gtk.DrawingArea):

def __init__(self):
super(Board, self).__init__()

self.modify_bg(gtk.STATE_NORMAL, gtk.gdk.Color(0, 0, 0))
self.set_size_request(WIDTH, HEIGHT)

self.connect("expose-event", self.expose)

self.init_game()

def on_timer(self):

if self.inGame:
self.check_apple()
self.check_collision()
self.move()
self.queue_draw()
return True
else:
return False

def init_game(self):

self.left = False
self.right = True
self.up = False
self.down = False
self.inGame = True
self.dots = 3

for i in range(self.dots):
x[i] = 50 - i * 10
y[i] = 50

try:
self.dot = cairo.ImageSurface.create_from_png("dot.png")
self.head = cairo.ImageSurface.create_from_png("head.png")
self.apple = cairo.ImageSurface.create_from_png("apple.png")
except Exception, e:
print e.message
sys.exit(1)

self.locate_apple()
glib.timeout_add(100, self.on_timer)

def expose(self, widget, event):

cr = widget.window.cairo_create()

if self.inGame:
cr.set_source_rgb(0, 0, 0)
cr.paint()

cr.set_source_surface(self.apple, self.apple_x, self.apple_y)
cr.paint()

for z in range(self.dots):
if (z == 0):
cr.set_source_surface(self.head, x[z], y[z])
cr.paint()
else:
cr.set_source_surface(self.dot, x[z], y[z])
cr.paint()
else:
self.game_over(cr)

def game_over(self, cr):

w = self.allocation.width / 2
h = self.allocation.height / 2

(x, y, width, height, dx, dy) = cr.text_extents("Game Over")

cr.set_source_rgb(65535, 65535, 65535)
cr.move_to(w - width/2, h)
cr.show_text("Game Over")
self.inGame = False

def check_apple(self):

if x == self.apple_x and y == self.apple_y:
self.dots = self.dots + 1
self.locate_apple()

def move(self):

z = self.dots

while z > 0:
x[z] = x[(z - 1)]
y[z] = y[(z - 1)]
z = z - 1

if self.left:
x -= DOT_SIZE

if self.right:
x += DOT_SIZE

if self.up:
y -= DOT_SIZE

if self.down:
y += DOT_SIZE

def check_collision(self):

z = self.dots

while z > 0:
if z > 4 and x == x[z] and y == y[z]:
self.inGame = False
z = z - 1

if y > HEIGHT - DOT_SIZE:
self.inGame = False

if y < 0:
self.inGame = False

if x > WIDTH - DOT_SIZE:
self.inGame = False

if x < 0:
self.inGame = False

def locate_apple(self):

r = random.randint(0, RAND_POS)
self.apple_x = r * DOT_SIZE
r = random.randint(0, RAND_POS)
self.apple_y = r * DOT_SIZE

def on_key_down(self, event):

key = event.keyval

if key == gtk.keysyms.Left and not self.right:
self.left = True
self.up = False
self.down = False

if key == gtk.keysyms.Right and not self.left:
self.right = True
self.up = False
self.down = False

if key == gtk.keysyms.Up and not self.down:
self.up = True
self.right = False
self.left = False

if key == gtk.keysyms.Down and not self.up:
self.down = True
self.right = False
self.left = False

class Snake(gtk.Window):

def __init__(self):
super(Snake, self).__init__()

self.set_title('Snake')
self.set_size_request(WIDTH, HEIGHT)
self.set_resizable(False)
self.set_position(gtk.WIN_POS_CENTER)

self.board = Board()
self.connect("key-press-event", self.on_key_down)
self.add(self.board)

self.connect("destroy", gtk.main_quit)
self.show_all()

def on_key_down(self, widget, event):

key = event.keyval
self.board.on_key_down(event)

Snake()
gtk.main()
```

First we will define some globals used in our game.

The `WIDTH` and `HEIGHT` constants determine the size of the Board. The `DOT_SIZE` is the size of the apple and the dot of the snake. The `ALL_DOTS` constant defines the maximum number of possible dots on the Board. The `RAND_POS` constant is used to calculate a random position of an apple. The `DELAY` constant determines the speed of the game.

```x =  * ALL_DOTS
y =  * ALL_DOTS
```

These two lists store x, y coordinates of all possible joints of a snake.

The `init_game()` method initialises variables, loads images and starts a timeout function.

```self.left = False
self.right = True
self.up = False
self.down = False
self.inGame = True
self.dots = 3
```

When the game starts, the snake has three joints. And it is heading to the right.

In the `move()` method we have the key algorithm of the game. To understand it, look at how the snakeis moving. You control the head of the snake. You can change its direction with the cursor keys. The rest of the joints move one position up the chain. The second joint moves where the first was, the third joint where the second was etc.

```while z > 0:
x[z] = x[(z - 1)]
y[z] = y[(z - 1)]
z = z - 1
```

This code moves the joints up the chain.

```if self.left:
x -= DOT_SIZE
```

Move the head to the left.

In the `checkCollision()` method, we determine if the snake has hit itself or one of the walls.

```while z > 0:
if z > 4 and x == x[z] and y == y[z]:
self.inGame = False
z = z - 1
```

We finish the game if the snake hits one of its joints with the head.

```if y > HEIGHT - DOT_SIZE:
self.inGame = False
```

We finish the game if the snake hits the bottom of the Board.

The `locate_apple()` method locates an apple randomly on the form.

```r = random.randint(0, RAND_POS)
```

We get a random number from 0 to RAND_POS - 1.

```self.apple_x = r * DOT_SIZE
...
self.apple_y = r * DOT_SIZE
```

These line set the x, y coordinates of the apple object.

```    self.connect("key-press-event", self.on_key_down)
...

def on_key_down(self, widget, event):

key = event.keyval
self.board.on_key_down(event)
```

We catch the key press event in the Snake class, and delegate the processing to the board object.

In the `on_key_dow()` method of the Board class, we determine which keys the player hit.

```if key == gtk.keysyms.Left and not self.right:
self.left = True
self.up = False
self.down = False
```

If we hit the left cursor key, we set `self.left` variable to True. This variable is used in the `move()` method to change coordinates of the snake object. Notice also that when the snake is heading to the right, we cannot turn immediately to the left. Figure: Snake

This was the Snake computer game programmed using PyGTK programming library.