Step 7 of 12

Write game.py and open a window

Now the most important file. Open bobgame/game.py

import pygame

from .settings import BG_COLOR, FPS, HEIGHT, WIDTH


class Game:
    def __init__(self) -> None:
        pygame.init()
        self.screen = pygame.display.set_mode((WIDTH, HEIGHT))
        pygame.display.set_caption("Bobgame")
        self.clock = pygame.time.Clock()
        self.running = True

    def step(self, dt: float) -> None:
        for event in pygame.event.get():
            if event.type == pygame.QUIT or (
                event.type == pygame.KEYDOWN and event.key == pygame.K_ESCAPE
            ):
                self.running = False
        self.screen.fill(BG_COLOR)
        pygame.display.flip()

    def run(self) -> None:
        while self.running:
            self.step(self.clock.tick(FPS) / 1000)
        pygame.quit()

That's a lot, so here it is piece by piece.

import pygame brings in the library. The line from .settings import ... brings in our own numbers from settings.py. The dot means "from the same folder".
class Game is a class, a blueprint. Imagine a blueprint for a house: it isn't a house, but you can build a house from it. Our blueprint describes a game.
__init__ runs once, the moment the game is built. It starts pygame, makes the window with set_mode, gives it a title, and creates a Clock, which keeps time so the game runs at the same speed on every computer. self just means "this game". self.running = True is a switch that says the game is on.
run is the game loop, the heart of every game. while self.running: means "keep repeating this for as long as running is True". Each lap of the loop is one frame, which is one picture of the flipbook. When the switch becomes False, the loop ends and pygame.quit() closes everything.
self.clock.tick(FPS) waits so we don't go faster than 60 laps a second, and tells us how many milliseconds that lap took. Dividing by 1000 turns it into seconds. We call that number dt (short for "delta time", or "the time since the last frame"). We'll use it soon.
step is what happens on each lap. First it checks the events, things that happened like a key press or clicking the window's close button. If you close the window (QUIT) or press Escape, we flip the switch to False. Then it paints the whole screen with the background colour, and display.flip() shows the finished picture.

The -> None and : float bits are called type hints. They are notes saying "this gives back nothing" and "this is a decimal number". Python doesn't need them, but they help you and VS Code understand the code.