《Python编程快速上手—让繁琐工作自动化》第15章实践项目答案

15.3 项目：超级秒表

项目要求：自己用 Python 写一个简单的秒表程序

#! python3
# A simple stopwatch program.

import time

print('Press ENTER to begin. Afterwards, press ENTER to "click" the stopwatch. Press Ctrl-C to quit.')
input()
print('Started.')
startTime = time.time()
lastTime = startTime
lapNum = 1

try:
    while True:
        input()
        laptime = round((time.time() - lastTime), 2)
        totalTime = round((time.time() - startTime), 2)
        print('Lap: %s; laptime: %s; totalTime: %s' % (lapNum, laptime, totalTime), end=' ')
        lapNum += 1
        lastTime = time.time()
except KeyboardInterrupt:
    print('\nDONE!')
    input('click any key to exit')

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15.7 项目：多线程 XKCD 下载程序

项目要求：多线程程序中有一些线程在下载漫画，同时另一些线程在建立连接，或将漫画图像文件写入硬盘。它更有效地使用 Internet 连接，更迅速地下载这些漫画。打开一个新的文件编辑器窗口，并保存为 multidownloadXkcd.py。你将修改这个程序，添加多线程。

#! python3
# Downloads XKCD comics using multiple threads.

import os, bs4, requests
urls = 'http://xkcd.com'
os.makedirs('xkcd', exist_ok = True)
def comic_download_kxcd(startComic, endComic):
    for num in range(startComic, endComic):
    # todo: download the page
        url = urls + '/%s/' % num
        print('Downloading page %s...' % url)
        res = requests.get(url)
        try:
            res.raise_for_status()
        except requests.exceptions.HTTPError:
            pass
        soup = bs4.BeautifulSoup(res.text, "html.parser")

    # todo: find the url of comic page
        comicElems = soup.select('#comic img')
        if comicElems == []:
            print('Could not find comic image!')
        else:
            comicUrl = 'http:' + comicElems[0].get('src')
    # todo: download the jpg
            print('Downloading image %s' % comicUrl)
            res = requests.get(comicUrl)
            res.raise_for_status()
    # todo: save jpg to ./xkcd
            image_name = os.path.join('xkcd', os.path.basename(comicUrl))
            with open(image_name, 'wb') as imageFile:
                for chunk in res.iter_content(100000):
                    imageFile.write(chunk)
    # todo: get the prev button's url
        prevLink = soup.select('a[rel="prev"]')[0]

# Create and start the Thread objects.
import threading
comic_threads = []
for i in range(1,1400,100):      # loops 14 times, creates 14 threads
    comic_thread = threading.Thread(target=comic_download_kxcd, args=(i, i+5)) 
    comic_threads.append(comic_thread)
    comic_thread.start()

# Wait for all threads to end.
for comic_thread in comic_threads:
    comic_thread.join()

print('Done.')

思路：

1. 多线程这个真的很惊艳，第一次接触会觉得“居然还有这种操作？！”
2. 按照书中步骤一步步码

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15.9 项目：简单的倒计时程序

项目要求：让我们来写一个倒计时程序，在倒计时结束时报警。

#! python3
# A simple countdown script.

import time, subprocess
while True:
    try:
        time_l = int(input('Please input a time(seconds): '))
    except Exception:
        print('number please!')
    else:
        break

while time_l > 0:
    print(time_l)       # 不知道为什么这里传入end=" "会不显示数字进行倒计时
    time.sleep(1)
    time_l = time_l - 1

print('\nalert!!')
time.sleep(2)
a = subprocess.Popen(['start','abc001.txt'], shell=True)

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15.12.1 实践项目：美化的秒表

项目要求：扩展本章的秒表项目，让它利用 rjust()和 ljust()字符串方法“美化”的输出。

#! python3
# A simple stopwatch program.

import time

print('Press ENTER to begin. Afterwards, press ENTER to "click" the stopwatch. Press Ctrl-C to quit.')
input()
print('Started.')
startTime = time.time()
lastTime = startTime
lapNum = 1

try:
    while True:
        input()
        laptime = round((time.time() - lastTime), 2)
        totalTime = round((time.time() - startTime), 2)
        print('Lap #' + str(lapNum).rjust(2) + ':' + ('%.2f'%totalTime).rjust(6) + 
        ' (' + ('%.2f'%laptime).rjust(5) +  ')',end=' ')
        lapNum += 1
        lastTime = time.time()
except KeyboardInterrupt:
    print('\nDONE!')
    input('click any key to exit')

15.12.2 实践项目：计划的 Web 漫画下载

• 容我偷个懒

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环境：python3

想做这个系列文章，就是因为当时看这本书时，想看看网上有没更优美的解决，但是略难找到。所以就把自己的项目练习放在了一个txt文件中，现在把练习代码放到这里，有不足之处希望大家能给出指导意见及相互交流、提升。