[PyGame] Cannot display anything inside pygame window

[deanhystad]

The function is not defined in the while loop, it is defined below the while loop. It is a convention to put the functions at the top of a module, but python doesn't care. Functions are compiled when the file is imported the first time, not during runtime, so it wouldn't matter if the function was defined in a loop.

Here's an example of how a snake game might be structured:

import pygame
from random import randint
 
CUBE_SIZE = 25
CUBES_NUM = 20
WIDTH = CUBE_SIZE * CUBES_NUM
 
 
class Segment(pygame.sprite.Sprite):
    """A segment of a snake"""
    def __init__(self, pos=(0, 0), color="green"):
        super().__init__()
        self.rect = pygame.Rect(0, 0, CUBE_SIZE, CUBE_SIZE)
        self.image = pygame.surface.Surface(self.rect.size)
        self.image.fill(color)
        self.at(list(pos))
 
    def at(self, position):
        """Set my grid location."""
        self.pos = position
        self.rect.x = self.pos[0] * CUBE_SIZE
        self.rect.y = self.pos[1] * CUBE_SIZE
 
    def draw(self, screen):
        """Draw self on screen."""
        screen.blit(self.image, self.rect)
 
 
class Food(Segment):
    """Something to eat."""
    def __init__(self):
        """I randomly place myself on the screen."""
        super().__init__([randint(1, CUBES_NUM - 2), randint(1, CUBES_NUM - 2)], "blue")
 
 
class Snake(pygame.sprite.Group):
    """A group of segments that moves in a coordinated fasion."""
    directions = ((1, 0), (0, 1), (-1, 0), (0, -1))
    colors = ("green", "yellow")
 
    def __init__(self, segments):
        """Initialize the sname.  segments is list of grid coordinates."""
        super().__init__()
        color = "red"
        for i, segment in enumerate(segments, start=1):
            self.add(Segment(segment, color))
            color = self.colors[i % len(self.colors)]
        self.head = self.sprites()[0]
        self.direction = 0
        self.add_segment = False
        self.score = 0
 
    def turn(self, turn):
        """Turn the snake left (-1) or right (1)."""
        self.direction = (self.direction + turn) % len(self.directions)
 
    def update(self):
        """Update all the segment positions."""
        segments = self.sprites()[::-1]
        if self.add_segment:
            # New segment is at the tail end of the snake.
            self.add_segment = False
            self.add(Segment(segments[0].pos, self.colors[len(segments) % 2]))
 
        # Move all the snake sgments.  Starting at the tail each segment moves
        # to the previous location of the next segment.
        for a, b in zip(segments, segments[1:]):
            a.at(b.pos)
        delta = self.directions[self.direction]
        self.head.at([self.head.pos[0] + delta[0], self.head.pos[1] + delta[1]])
 
        # Check if the snake hit a wall
        pos = snake.head.pos
        if min(pos) < 0 or max(pos) >= CUBES_NUM:
            self.kill()
            return
 
        # Check if snake bit itself.
        for segment in segments[:-1]:
            if segment.pos == pos:
                self.kill()
                return
 
    def eats(self, food):
        """Return True if snake eats food."""
        if len(self) > 0 and self.head.pos == food.pos:
            self.score += 1
            food.kill()
            self.add_segment = True  # Snake grows longer when it eats.
            return True
        return False
 
    def kill(self):
        """Kill all the segments."""
        for segment in self.sprites():
            segment.kill()
 
 
pygame.init()
screen = pygame.display.set_mode((WIDTH, WIDTH))
clock = pygame.time.Clock()
snake = Snake([(x, 10) for x in range(10, 16)])
snake.direction = 2
food = Food()
speed = 4
while len(snake) > 0:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            snake.kill()
        elif event.type == pygame.KEYDOWN:
            if event.key == pygame.K_LEFT:
                snake.turn(-1)
            elif event.key == pygame.K_RIGHT:
                snake.turn(1)
 
    snake.update()
    if snake.eats(food):
        speed += 1
        food = Food()
 
    screen.fill("white")
    food.draw(screen)
    snake.draw(screen)
    pygame.display.update()
    clock.tick(speed)

print("Your score =", snake.score)

I left out all the challenging parts like multiple plays and leaderboards, but it is enough to give you an idea about how a snake like game can be designed. You don't have to use sprites and groups, but I think programming a game is much simpler if you do.