【廖雪峰Python习题集】常用内建模块

datetime：

假设你获取了用户输入的日期和时间如2015-1-21 9:01:30，以及一个时区信息如UTC+5:00，均是str，请编写一个函数将其转换为timestamp：

import  refrom  datetime import  datetime,timezone,timedeltadef to_timestamp(dt_str,tz_str):    #str转换为datetime    cday = datetime.strptime(dt_str, '%Y-%m-%d %H:%M:%S')    t = tz_str.split('C')    t2 = t[1].split(':')    hour = int(t2[0])    mine = int(t2[1])    #创建时区UTC时间    tz_utc = timezone(timedelta(hours=hour,minutes=mine))    #强制设置UTC时间    dt = cday.replace(tzinfo=tz_utc)    #返回timestamp时间    return dt.timestamp()if __name__ == "__main__":    t1 = to_timestamp('2015-6-1 08:10:30','UTC+7:00')    assert t1 == 1433121030.0 ,t1    t2 = to_timestamp('2015-5-31 16:10:30', 'UTC-09:00')    assert t2 == 1433121030.0 , t2    print('Pass')

显示结果如下图所示：

base64：

请写一个能处理去掉=的base64解码函数：

import  base64def safe_base64_decode(s):    if not s.__contains__(b'=='):        s = s + b'=='    return base64.b64decode(s)if __name__ =="__main__":    assert b'abcd' == safe_base64_decode(b'YWJjZA==') ,safe_base64_decode('YWJjZA==')    assert b'abcd' == safe_base64_decode(b'YWJjZA') , safe_base64_decode('YWJjZA')    print('Pass')

显示结果如下图所示：

struct:

请编写一个bmpinfo.py，可以检查任意文件是否是位图文件，如果是，打印出图片大小和颜色数：

import structdef bmpinfo(str):    f = open(str, 'rb')    s = f.read(30)    h = struct.unpack('<ccIIIIIIHH', s)    if h[0] == b'B' and (h[1] == b'M' or h[1] == b'A'):        print(True)        print('位图大小：', h[6], '*', h[7], '颜色数：', h[9])    else:        print(False)        if __name__ == "__main__":    str = input('please the way of your file')    bmpinfo(str)

显示结果如下图所示：

#是位图文件时：

#不是位图文件时：

hashlib:

练习1：

根据用户输入的口令，计算出存储在数据库中的MD5口令：

def calc_md5(password):    pass

存储MD5的好处是即使运维人员能访问数据库，也无法获知用户的明文口令。

设计一个验证用户登录的函数，根据用户输入的口令是否正确，返回True或False：

db = {    'michael': 'e10adc3949ba59abbe56e057f20f883e',    'bob': '878ef96e86145580c38c87f0410ad153',    'alice': '99b1c2188db85afee403b1536010c2c9'}def login(user, password):    pass

采用MD5存储口令是否就一定安全呢？也不一定。假设你是一个黑客，已经拿到了存储MD5口令的数据库，如何通过MD5反推用户的明文口令呢？暴力破解费事费力，真正的黑客不会这么干。

考虑这么个情况，很多用户喜欢用123456，888888，password这些简单的口令，于是，黑客可以事先计算出这些常用口令的MD5值，得到一个反推表：

'e10adc3949ba59abbe56e057f20f883e': '123456''21218cca77804d2ba1922c33e0151105': '888888''5f4dcc3b5aa765d61d8327deb882cf99': 'password'

这样，无需破解，只需要对比数据库的MD5，黑客就获得了使用常用口令的用户账号。

对于用户来讲，当然不要使用过于简单的口令。但是，我们能否在程序设计上对简单口令加强保护呢？

由于常用口令的MD5值很容易被计算出来，所以，要确保存储的用户口令不是那些已经被计算出来的常用口令的MD5，这一方法通过对原始口令加一个复杂字符串来实现，俗称“加盐”：

def calc_md5(password):    return get_md5(password + 'the-Salt')

经过Salt处理的MD5口令，只要Salt不被黑客知道，即使用户输入简单口令，也很难通过MD5反推明文口令。

但是如果有两个用户都使用了相同的简单口令比如123456，在数据库中，将存储两条相同的MD5值，这说明这两个用户的口令是一样的。有没有办法让使用相同口令的用户存储不同的MD5呢？

如果假定用户无法修改登录名，就可以通过把登录名作为Salt的一部分来计算MD5，从而实现相同口令的用户也存储不同的MD5。

import hashlibdef get_md5(str):    md5 = hashlib.md5()    md5.update(str.encode('utf-8'))    return md5.hexdigest()def calc_md5(password):    return get_md5(password)db = {    'michael':'e10adc3949ba59abbe56e057f20f883e',    'bob':'878ef96e86145580c38c87f0410ad153',    'alice':'99b1c2188db85afee403b1536010c2c9'}def login(user,password):    if db[user] == password:        return True    else:        return Falseif __name__ == "__main__":    username = input('please input username:')    password = input('please input password:')    pwd = calc_md5(password)    print(login(username,pwd))

显示结果如下图所示：

练习2：

根据用户输入的登录名和口令模拟用户注册，计算更安全的MD5：

db = {}

def register(username,password):

      dn[username]  = get_md5(password + username + 'the-Salt')

然后，根据修改后的MD5算法实现用户登录的验证：

 def login(username,password):

      pass

import hashlibdef get_md5(str):    md5 = hashlib.md5()    md5.update(str.encode('utf-8'))    return md5.hexdigest()db = {}def register(username,password):    db[username] = get_md5(password + username + 'the-Salt')def login(username,password):    pwd = get_md5(password + username + 'the-Salt')    if db[username] ==  pwd:        return True    else:        return Falseif __name__ == "__main__":    username = input('please input username:')    password = input('please input password:')    register(username,password)    print(login(username,password))

显示结果如下图所示：

XML:

请利用SAX编写程序解析Yahoo的XML格式的天气预报，获取当天和第二天的天气：

http://weather.yahooapis.com/forecastrss?u=c&w=2151330

参数w是城市代码，要查询某个城市代码，可以在weather.yahoo.com搜索城市，浏览器地址栏的URL就包含城市代码

from xml.parsers.expat import  ParserCreateweather_dict = {}which_day = 0class WeatherSaxHandler(object):    def start_element(self,name,attrs):        global  weather_dict,which_day        if name=='yweather:location':            weather_dict['city']=attrs['city']            weather_dict['country'] = attrs['country']        if name == 'yweather:forecast':            which_day+=1            if which_day == 1 :                weather = {                    'text':attrs['text'],                    'low':int(attrs['low']),                    'high':int(attrs['high'])                }                weather_dict['today'] = weather            elif which_day == 2:                weather={                    'text': attrs['text'],                    'low':int(attrs['low']),                    'high':int(attrs['high'])                }                weather_dict['tomorrow'] = weather    def char_data(self,name):        pass    def end_element(self,text):        passdef parse_weather(xml):    wea = WeatherSaxHandler()    parser = ParserCreate()    parser.StartElementHandler = wea.start_element    parser.EndElementHandler = wea.end_element    parser.CharacterDataHandler = wea.char_data    parser.Parse(xml)    return weather_dictdata = r'''<?xml version="1.0" encoding="UTF-8" standalone="yes" ?><rss version="2.0" xmlns:yweather="http://xml.weather.yahoo.com/ns/rss/1.0" xmlns:geo="http://www.w3.org/2003/01/geo/wgs84_pos#">    <channel>        <title>Yahoo! Weather - Beijing, CN</title>        <lastBuildDate>Wed, 27 May 2015 11:00 am CST</lastBuildDate>        <yweather:location city="Beijing" region="" country="China"/>        <yweather:units temperature="C" distance="km" pressure="mb" speed="km/h"/>        <yweather:wind chill="28" direction="180" speed="14.48" />        <yweather:atmosphere humidity="53" visibility="2.61" pressure="1006.1" rising="0" />        <yweather:astronomy sunrise="4:51 am" sunset="7:32 pm"/>        <item>            <geo:lat>39.91</geo:lat>            <geo:long>116.39</geo:long>            <pubDate>Wed, 27 May 2015 11:00 am CST</pubDate>            <yweather:condition text="Haze" code="21" temp="28" date="Wed, 27 May 2015 11:00 am CST" />            <yweather:forecast day="Wed" date="27 May 2015" low="20" high="33" text="Partly Cloudy" code="30" />            <yweather:forecast day="Thu" date="28 May 2015" low="21" high="34" text="Sunny" code="32" />            <yweather:forecast day="Fri" date="29 May 2015" low="18" high="25" text="AM Showers" code="39" />            <yweather:forecast day="Sat" date="30 May 2015" low="18" high="32" text="Sunny" code="32" />            <yweather:forecast day="Sun" date="31 May 2015" low="20" high="37" text="Sunny" code="32" />        </item>    </channel></rss>'''if __name__ == "__main__":    weather = parse_weather(data)    assert weather['city'] == 'Beijing', weather['city']    assert weather['country'] == 'China', weather['country']    assert weather['today']['text'] == 'Partly Cloudy', weather['today']['text']    assert weather['today']['low'] == 20, weather['today']['low']    assert weather['today']['high'] == 33, weather['today']['high']    assert weather['tomorrow']['text'] == 'Sunny', weather['tomorrow']['text']    assert weather['tomorrow']['low'] == 21, weather['tomorrow']['low']    assert weather['tomorrow']['high'] == 34, weather['tomorrow']['high']    print('Weather:', str(weather))

显示结果如下图所示：

HTMLParser:

找一个网页，例如：https://www.python.org/events/python-events，用浏览器查看源码并复制，然后尝试解析一下HTML，输出Python官网发布的会议时间，名称和地点

from html.parser import HTMLParserfrom  html.entities import  name2codepointfrom urllib import request,parseclass MyHTMLParser(HTMLParser):    in_title = False    in_loca = False    in_time = False    times = []    def handle_starttag(self, tag, attrs):        if ('class','event-title') in attrs:            self.in_title =True        elif ('class','event-location') in attrs:            self.in_loca = True        elif tag =='time':            self.in_time = True            self.times=[]    def handle_endtag(self, tag):        if tag == 'h3':self.in_title = False        if  tag =='span':self.in_loca = False        if tag =='time':            self.in_time = False            print('Time:'+'-'.join(self.times))    def handle_startendtag(self, tag, attrs):        pass    def handle_data(self, data):        if self.in_title:            print('Title: '+data.strip())        if self.in_loca:            print('Location: '+data.strip())        if self.in_time:            self.times.append(data)    def handle_comment(self, data):        pass    def handle_entityref(self, name):        pass    def handle_charref(self, name):        passif __name__ == "__main__":    with request.urlopen('https://www.python.org/events/python-events') as f:        data=f.read()        req = data.decode('utf-8')    parser = MyHTMLParser()    parser.feed(req)

显示结果如下图所示：

F:\SoftWare\Python3.6\python.exe F:/SoftWare/Python3.6/Lib/urllib/explainHtml.pyTitle: Django Girls KoforiduaTime:11 Nov. – 12 Nov. - 2017Location: Koforidua, GhanaTitle: PuPPy, Seattle's Python user group's monthly meetingTime:11 Nov.- 2017Location: Seattle Humane, 13212 SE Eastgate Way, Bellevue, WA 98005, USATitle: PyHPC 2017: 7th Workshop on Python for High-Performance and Scientific ComputingTime:12 Nov. – 13 Nov. - 2017Location: Denver, CO, USATitle: PyRoma MeetupTime:14 Nov.- 2017Location: Rome, ItalyTitle: PyCon Jamaica 2017Time:16 Nov. – 19 Nov. - 2017Location: Kingston, JamaicaTitle: PyConAr 2017Time:17 Nov. – 20 Nov. - 2017Location: Haya De La Torre S/N, Córdoba, Cordoba, ArgentinaTitle: Django Girls Santa BarbaraTime:18 Nov. – 19 Nov. - 2017Location: UCSB, Santa Barbara, CaliforniaTitle: PyTexas 2017Time:18 Nov. – 19 Nov. - 2017Location: 119 Nueces St, Austin, TX 78701, USATitle: PyCon Canada 2017Time:18 Nov. – 22 Nov. - 2017Location: Montreal, Quebec, CanadaTitle: SciPy India 2017Time:29 Nov. – 01 Dec. - 2017Location: LCH, IIT Bombay, Powai, Mumbai, IndiaTitle: Kiwi PyCon 2017Time:02 Dec. – 04 Dec. - 2017Location: Auckland, New ZealandTitle: Django Girls Pereira, ColombiaTime:02 Dec. – 03 Dec. - 2017Location: Pereira, ColombiaTitle: Django Girls IbaguéTime:02 Dec. – 03 Dec. - 2017Location: Ibagué, ColombiaTitle: North Bay Python 2017Time:02 Dec. – 04 Dec. - 2017Location: Petaluma, California, USATitle: PyCon Indonesia 2017Time:09 Dec. – 10 Dec. - 2017Location: Surabaya, IndonesiaTitle: Indy Startup Row Pitch EventTime:09 Jan. – 10 Jan. - 2018Location: Indianapolis, IN, USTitle: Python Meeting Düsseldorf (PyDDF)Time:17 Jan.- 2018Location: Bürgerhaus, Bachstr. 145, 40217 DüsseldorfTitle: PyCascades 2018Time:22 Jan. – 24 Jan. - 2018Location: Vancouver, BC V6A, CanadaTitle: PyCon Cameroon 2018Time:24 Jan. – 29 Jan. - 2018Location: Limbe, CameroonTitle: Pythology One-Day Conference: Security Best PracticesTime:02 Feb. – 03 Feb. - 2018Location: Fishers, IN, USATitle: FOSDEM 2018Time:03 Feb. – 05 Feb. - 2018Location: ULB Campus du Solbosch, Av. F. D. Roosevelt 50, 1050 Bruxelles, BelgiumTitle: PyCon Pune 2018Time:08 Feb. – 12 Feb. - 2018Location: Pune, IndiaTitle: PyCon Colombia 2018Time:09 Feb. – 12 Feb. - 2018Location: Medellin, ColombiaTitle: PyCon SK 2018Time:09 March – 12 March - 2018Location: Bratislava, SlovakiaTitle: PyCon IT 9Time:19 April – 23 April - 2018Location: Hotel Mediterraneo - Lungarno del Tempio, 44, 50121 Firenze FI, ItalyTitle: GeoPython 2018Time:07 May – 10 May - 2018Location: Basel, SwitzerlandTitle: PyCon US 2018Time:09 May – 18 May - 2018Location: Cleveland, Ohio, USATitle: PyCon US 2019Time:01 May – 10 May - 2019Location: Cleveland, Ohio, USAProcess finished with exit code 0

urllib:

利用urllib读取XML，将XML一节的数据由硬编码改为由urllib获取：