pong in python

#!/usr/bin/python3
# coding: utf-8
import constant
import pygame


class Keyboard:
    def listen_keys(self):
        pygame.event.pump()
        keys = pygame.key.get_pressed()
        keys_players = {
                        self.player_one: { pygame.K_w: -10, pygame.K_s: +10},
                        self.player_two: { pygame.K_UP: -10, pygame.K_DOWN: +10}
        }
        for player,v in keys_players.items():
            for key_number,add in keys_players[player].items():
                if keys[key_number]:
                    player.move(add)
                if keys[pygame.K_r] and self.ball_tmp is not None:
                    self.ball = self.ball_tmp
                    self.ball_tmp = None
                    self.init_settings()


class Ball:
    def __init__(self, pos_x, pos_y):
        self.x, self.y = pos_x, pos_y
        self.xspeed, self.yspeed = 5, 0
        self.width, self.height = 20, 20
        self.last_move = pygame.time.get_ticks()
        self.last_player_touched = None

    def draw(self, surface):
        self.rect = pygame.draw.rect(surface, (constant.WHITE), (self.x, self.y,
                                                                    self.width, self.height))

    def move(self):
        diff = (pygame.time.get_ticks() - self.last_move)
        if diff > 0.3: # each 0,3*10**-3μs move
            self.yspeed = +5 if self.y <= 0 else self.yspeed
            self.yspeed = -5 if self.y >= (constant.HEIGHT - self.height) else self.yspeed
            if (self.x >= 0) and (self.x <= constant.WIDTH):
                self.x += self.xspeed
            if (self.y >= -constant.HEIGHT) and (self.y <= constant.HEIGHT):
                self.y += self.yspeed
            self.last_move = pygame.time.get_ticks()

    def collide_with(self, *players):
        for player in players:
            if player.rect.colliderect(self.rect):
                self.last_player_touched = player
                self.xspeed = abs(self.xspeed) if player.x < 30 else -abs(self.xspeed)
                self.yspeed = ((self.y**1.3) - (player.y**1.3)) / player.height

    def has_gone(self):
        if (self.x <= self.width) or (self.x >= constant.WIDTH):
            return True

class Player:
    def __init__(self, pos_x, pos_y, name):
        self.name = name
        self.width, self.height = 10, 100
        self.x, self.y = pos_x, (pos_y - (self.height // 2))

    def draw(self, surface):
        self.rect = pygame.draw.rect(surface, (constant.WHITE), (self.x, self.y,
                                                        self.width, self.height))

    def move(self, y):
        if (self.y + y > self.width) and ((self.y + y) < constant.HEIGHT - (self.height + self.width)):
            self.y += y


class Game(Keyboard):
    def __init__(self):
        pygame.init()
        pygame.font.init()
        pygame.display.set_caption("Pong in Python")
        pygame.event.set_allowed([pygame.QUIT, pygame.KEYDOWN])
        self._game_border = 25
        self.font = pygame.font.Font(pygame.font.get_default_font(), 32)
        self.screen = pygame.display.set_mode(constant.SIZE, pygame.DOUBLEBUF)
        self.screen.set_alpha(None)
        self.ball = Ball(self.on_center(constant.WIDTH), self.on_center(constant.HEIGHT))
        self.ball_tmp = None
        self.player_one = Player(self._game_border, self.on_center(constant.HEIGHT), "1")
        self.player_two = Player(constant.WIDTH - self._game_border, self.on_center(constant.HEIGHT), "2")
        self.init_settings()
        self.start()

    def on_center(self, size):
        return size // 2

    def init_settings(self):
        self.ball.x, self.ball.y = self.on_center(constant.WIDTH), self.on_center(constant.HEIGHT)
        self.player_one_x, self.player_one_y = self._game_border, self.on_center(constant.HEIGHT)
        self.player_two_x, self.player_two_y = constant.WIDTH - self._game_border, self.on_center(constant.HEIGHT)

    def start(self):
        while True:
            try:
                if pygame.event.get(pygame.QUIT): break
                self.screen.fill(constant.BLACK)
                self.ball.draw(self.screen)
                self.ball.move()
                self.player_one.draw(self.screen)
                self.player_two.draw(self.screen)
                self.ball.collide_with(self.player_one, self.player_two)
                if self.ball.has_gone():
                    self.ball_tmp = self.ball
                    del self.ball
            except AttributeError as e:
                someone_wins = self.font.render("player {} wins!".format(self.ball_tmp.last_player_touched.name), True, (constant.WHITE))
                info = self.font.render("press R to restart", True, (constant.WHITE))
                self.screen.blit(someone_wins, (self.on_center(constant.WIDTH) - 100, 50))
                self.screen.blit(info, (self.on_center(constant.WIDTH) - 115, 100))
            finally:
                self.listen_keys()
                pygame.display.flip()

if __name__ == '__main__':
    Game()