Python - Pygame - simple template with classes

#!/usr/bin/env python3

# ---------------------------------------------------------------------
# pygame (simple) template with classes (by furas)
# ---------------------------------------------------------------------

import pygame
#import random

# === CONSTANTS ===

BLACK = (  0,   0,   0)
WHITE = (255, 255, 255)

RED   = (255,   0,   0)
GREEN = (  0, 255,   0)
BLUE  = (  0,   0, 255)

SCREEN_WIDTH  = 800
SCREEN_HEIGHT = 600

BLOCK_SIZE = 50

# === CLASSES ===

class StartState():

    def __init__(self, screen):
        self.screen = screen
        self.screen_rect = self.screen.get_rect()

        self.font_30 = pygame.font.SysFont(None, 30)
        self.font_50 = pygame.font.SysFont(None, 50)

        self.text_start = self.font_50.render("START", True, GREEN)
        self.text_start_rect = self.text_start.get_rect()
        # center on screen
        self.text_start_rect.center = self.screen_rect.center

        self.text_press = self.font_30.render("PRESS ANY KEY", True, WHITE)
        self.text_press_rect = self.text_press.get_rect()
        # middle bottom screen
        self.text_press_rect.midbottom = self.screen_rect.midbottom


    def draw(self):
        self.screen.fill(BLACK)
        self.screen.blit(self.text_start, self.text_start_rect)
        self.screen.blit(self.text_press, self.text_press_rect)

    def update(self):
        # TODO: move object, etc. (without drawing)
        pass

    def event_handle(self, event):
        # press any key
        if event.type == pygame.KEYDOWN:
            self.running = False

    def mainloop(self):

        self.clock = pygame.time.Clock()

        self.running = True

        while self.running:

            # --- events ---

            for event in pygame.event.get():

                # --- global events ---

                if event.type == pygame.QUIT:
                    self.running = False
                elif event.type == pygame.KEYDOWN:
                    if event.key == pygame.K_ESCAPE:
                        self.running = False

                # --- local events ---

                self.event_handle(event)

            # --- updates ---

            self.update()

            # --- draws ---

            self.draw()

            pygame.display.flip()

            # --- FPS ---

            self.clock.tick(25)

        return True

class EndState():

    def __init__(self, screen):
        self.screen = screen
        self.screen_rect = self.screen.get_rect()

        self.font_30 = pygame.font.SysFont(None, 30)
        self.font_50 = pygame.font.SysFont(None, 50)

        self.text = self.font_50.render("END", True, RED)
        self.text_rect = self.text.get_rect()
        # center on screen
        self.text_rect.center = self.screen_rect.center

        self.text_press = self.font_30.render("PRESS ANY KEY", True, WHITE)
        self.text_press_rect = self.text_press.get_rect()
        # middle bottom screen
        self.text_press_rect.midbottom = self.screen_rect.midbottom


    def draw(self):
        self.screen.fill(BLACK)
        self.screen.blit(self.text, self.text_rect)
        self.screen.blit(self.text_press, self.text_press_rect)

    def update(self):
        # TODO: move object, etc. (without drawing)
        pass

    def event_handle(self, event):
        if event.type == pygame.KEYDOWN:
            self.running = False

    def mainloop(self):

        self.clock = pygame.time.Clock()

        self.running = True

        while self.running:

            # --- events ---

            for event in pygame.event.get():

                # --- global events ---

                if event.type == pygame.QUIT:
                    self.running = False
                elif event.type == pygame.KEYDOWN:
                    if event.key == pygame.K_ESCAPE:
                        self.running = False

                # --- local events ---

                self.event_handle(event)

            # --- updates ---

            self.update()

            # --- draws ---

            self.draw()

            pygame.display.flip()

            # --- FPS ---

            self.clock.tick(25)

        return True

class GameState():

    def __init__(self, screen):
        self.screen = screen
        self.screen_rect = self.screen.get_rect()

        self.player = pygame.Surface((BLOCK_SIZE, BLOCK_SIZE))
        self.player.fill(GREEN)
        self.player_rect = self.player.get_rect()
        self.player_rect.center = self.screen_rect.center

        self.player_move_x = 0
        self.player_move_y = 0

        self.font_30 = pygame.font.SysFont(None, 30)

        self.text_press = self.font_30.render("PRESS 'ESCAPE' TO EXIT", True, WHITE)
        self.text_press_rect = self.text_press.get_rect()
        # middle bottom screen
        self.text_press_rect.midbottom = self.screen_rect.midbottom

        self.text_arrows = self.font_30.render("USE 'ARROWS' TO MOVE OBJECT", True, WHITE)
        self.text_arrows_rect = self.text_arrows.get_rect()
        # middle top screen
        self.text_arrows_rect.midtop = self.screen_rect.midtop

    def draw(self):
        self.screen.fill(BLACK)
        self.screen.blit(self.player, self.player_rect)
        self.screen.blit(self.text_press, self.text_press_rect)
        self.screen.blit(self.text_arrows, self.text_arrows_rect)

    def update(self):
        # --- updates ---

        self.player_rect.x += self.player_move_x
        self.player_rect.y += self.player_move_y

        self.player_rect.clamp_ip(self.screen_rect)


    def event_handle(self, event):
        # --- player events ---

        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_LEFT:
                self.player_move_x -= 10
            elif event.key == pygame.K_RIGHT:
                self.player_move_x += 10
            elif event.key == pygame.K_UP:
                self.player_move_y -= 10
            elif event.key == pygame.K_DOWN:
                self.player_move_y += 10

        elif event.type == pygame.KEYUP:
            if event.key == pygame.K_LEFT:
                self.player_move_x += 10
            elif event.key == pygame.K_RIGHT:
                self.player_move_x -= 10
            elif event.key == pygame.K_UP:
                self.player_move_y += 10
            elif event.key == pygame.K_DOWN:
                self.player_move_y -= 10


    def mainloop(self):

        self.clock = pygame.time.Clock()

        self.running = True

        while self.running:

            # --- events ---

            for event in pygame.event.get():

                # --- global events ---

                if event.type == pygame.QUIT:
                    self.running = False
                elif event.type == pygame.KEYDOWN:
                    if event.key == pygame.K_ESCAPE:
                        self.running = False

                # --- local events ---

                self.event_handle(event)

            # --- updates ---

            self.update()

            # --- draws ---

            self.draw()

            pygame.display.flip()

            # --- FPS ---

            self.clock.tick(25)

        return True

# === FUNCTIONS ===

# empty

# === MAIN ===

# --- init (only once for all classes) ---

pygame.init()

screen = pygame.display.set_mode((SCREEN_WIDTH, SCREEN_HEIGHT))

# --- states (almost "finite states machine" [FSM])---

result = StartState(screen).mainloop()

if result:
    result = GameState(screen).mainloop()

if result:
    result = EndState(screen).mainloop()

# --- the end (only once for all classes) ---

pygame.quit()