现在写书的人真是一点责任心都没有，最近看了几本书，其中的代码都存在错误。

最近迷恋 Python 游戏，买了《Python游戏编程入门》[美] Jonathan S·Harbour 著 一书来看。

其中第四章：Bomb Catcher游戏中，测试打字速度的程序代码严重有误。

改程序屏幕上随机显示一个字母，按键输入该字母后随机显示下一个，计算平均一分钟可以输入多少个字母，原代码中计算速度的一块有误，附上我修改后的代码

import sys
import random
import time
import pygame
from pygame.locals import *


def print_text(font, x, y, text, color=(255, 255, 255)):
    imgText = font.render(text, True, color)
    screen.blit(imgText, (x, y))


pygame.init()
screen = pygame.display.set_mode((600, 500))
pygame.display.set_caption('Keyboard Demo')
font1 = pygame.font.Font(None, 24)
font2 = pygame.font.Font(None, 200)
white = (255, 255, 255)
yellow = (255, 255, 0)

key_flag = False
correct_answer = 97     # a
seconds = 11
score = 0
speed = 0
clock_start = 0
game_over = True

while True:
    for event in pygame.event.get():
        if event.type == QUIT:
            sys.exit()
        elif event.type == KEYDOWN:
            key_flag = True
        elif event.type == KEYUP:
            key_flag = False

    keys = pygame.key.get_pressed()     # keys 是一个元组，穷举了所有的按键，未按下为 0，按下为 1
    if keys[K_ESCAPE]:
        sys.exit()
    if keys[K_RETURN]:
        if game_over:
            game_over = False
            clock_start = time.time()
            score = 0
            seconds = 11
            speed = 0
            clock = clock_start

    if not game_over:
        current = time.time() - clock_start
        if seconds < current:
            game_over = True
        else:
            if keys[correct_answer]:
                correct_answer = random.randint(97, 122)
                clock_start = time.time()
                score += 1
                speed = 60 * score / (clock_start - clock)

    screen.fill((0, 100, 0))
    print_text(font1, 0, 0, "Let's see how fast you can type!")
    print_text(font1, 0, 20, "Try to keep up for 10 seconds...")

    if key_flag:
        print_text(font1, 500, 0, "<key>")

    if not game_over:
        print_text(font1, 0, 80, "Time: " + str(int(seconds-current)))

    print_text(font1, 0, 100, "Speed: " + str(int(speed)) + " letters/min")

    if game_over:
        print_text(font1, 0, 160, "Press Enter to start...")

    print_text(font2, 0, 240, chr(correct_answer-32), yellow)

    pygame.display.update()