对howdoi的一个简单分析。

曾经看到过下面的这样一段js代码：

try{doSth();
}
catch (e){ask_url = "https://stackoverflow.com/search?q="window.location.href= ask_url + encodeURIComponent(e)
}

howdoi基本就是把这个流程做成了Python脚本。其基本流程如下：

• step1：利用site语法组装搜索语句(默认指定搜索stackoverflow网站)
• step2:利用google搜索接口获取搜索引擎第一页排名第一的连接
• step3：访问该链接，根据排名从高倒下，提取代码块文本
• step4：提取到就显示到终端，没有提取到就提示未找到答案

当然，howdoi也作了一些其他的工作：

• 代理设置
• 既往问题进行缓存，提高下次查询的速度
• 查询的目标网站可配置
• 做成Python script脚本命令，方便快捷
• 代码高亮格式化输出

更多分析请看代码注释：

!/usr/bin/env python######################################################
#
# howdoi - instant coding answers via the command line
# written by Benjamin Gleitzman (gleitz@mit.edu)
# inspired by Rich Jones (rich@anomos.info)
#
######################################################import argparse #用于获取脚本命令行参数
import glob
import os
import random
import re
import requests #用于发送http(s)请求
import requests_cache
import sys
from . import __version__
#用于控制台彩色高亮格式化输出
from pygments import highlight
from pygments.lexers import guess_lexer, get_lexer_by_name
from pygments.formatters.terminal import TerminalFormatter
from pygments.util import ClassNotFound
# 用于网页解析
from pyquery import PyQuery as pqfrom requests.exceptions import ConnectionError
from requests.exceptions import SSLError# 兼容Python2.x和Python3.x的库
if sys.version < '3':import codecsfrom urllib import quote as url_quotefrom urllib import getproxies# 处理unicode: http://stackoverflow.com/a/6633040/305414def u(x):return codecs.unicode_escape_decode(x)[0]
else:from urllib.request import getproxiesfrom urllib.parse import quote as url_quotedef u(x):return x#设置google搜索url
if os.getenv('HOWDOI_DISABLE_SSL'):  # 使用系统环境变量中非SSL的http代替httpsSEARCH_URL = 'http://www.google.com/search?q=site:{0}%20{1}'VERIFY_SSL_CERTIFICATE = False
else:SEARCH_URL = 'https://www.google.com/search?q=site:{0}%20{1}'VERIFY_SSL_CERTIFICATE = True
#设置目标问答网站
URL = os.getenv('HOWDOI_URL') or 'stackoverflow.com'#浏览器UA，用于伪造浏览器请求，防止网站对脚本请求进行屏蔽
USER_AGENTS = ('Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:11.0) Gecko/20100101 Firefox/11.0','Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:22.0) Gecko/20100 101 Firefox/22.0','Mozilla/5.0 (Windows NT 6.1; rv:11.0) Gecko/20100101 Firefox/11.0',('Mozilla/5.0 (Macintosh; Intel Mac OS X 10_7_4) AppleWebKit/536.5 (KHTML, like Gecko) ''Chrome/19.0.1084.46 Safari/536.5'),('Mozilla/5.0 (Windows; Windows NT 6.1) AppleWebKit/536.5 (KHTML, like Gecko) Chrome/19.0.1084.46''Safari/536.5'), )
#格式化答案输出
ANSWER_HEADER = u('--- Answer {0} ---\n{1}')
NO_ANSWER_MSG = '< no answer given >'#设置缓存文件路径
XDG_CACHE_DIR = os.environ.get('XDG_CACHE_HOME',os.path.join(os.path.expanduser('~'), '.cache'))
CACHE_DIR = os.path.join(XDG_CACHE_DIR, 'howdoi')
CACHE_FILE = os.path.join(CACHE_DIR, 'cache{0}'.format(sys.version_info[0] if sys.version_info[0] == 3 else ''))#获取代理（在国内China尤其有用，不解释）
def get_proxies():proxies = getproxies()filtered_proxies = {}for key, value in proxies.items():if key.startswith('http'):if not value.startswith('http'):filtered_proxies[key] = 'http://%s' % valueelse:filtered_proxies[key] = valuereturn filtered_proxiesdef _get_result(url):try:return requests.get(url, headers={'User-Agent': random.choice(USER_AGENTS)}, proxies=get_proxies(),verify=VERIFY_SSL_CERTIFICATE).textexcept requests.exceptions.SSLError as e:print('[ERROR] Encountered an SSL Error. Try using HTTP instead of ''HTTPS by setting the environment variable "HOWDOI_DISABLE_SSL".\n')raise e# 获取google搜索结果中的连接
def _get_links(query):result = _get_result(SEARCH_URL.format(URL, url_quote(query)))html = pq(result)#用pyquery进行解析return [a.attrib['href'] for a in html('.l')] or \[a.attrib['href'] for a in html('.r')('a')]def get_link_at_pos(links, position):if not links:return Falseif len(links) >= position:link = links[position - 1]else:link = links[-1]return link#代码格式化输出函数
def _format_output(code, args):if not args['color']:return codelexer = None# try to find a lexer using the StackOverflow tags# or the query argumentsfor keyword in args['query'].split() + args['tags']:try:lexer = get_lexer_by_name(keyword)breakexcept ClassNotFound:pass# no lexer found above, use the guesserif not lexer:try:lexer = guess_lexer(code)except ClassNotFound:return codereturn highlight(code,lexer,TerminalFormatter(bg='dark'))#利用政策匹配判断连接是否是问题
def _is_question(link):return re.search('questions/\d+/', link)#获取问题连接
def _get_questions(links):return [link for link in links if _is_question(link)]#获取答案（主要是解析stackoverflow的问答页面）
def _get_answer(args, links):links = _get_questions(links)link = get_link_at_pos(links, args['pos'])if not link:return Falseif args.get('link'):return linkpage = _get_result(link + '?answertab=votes')html = pq(page)first_answer = html('.answer').eq(0)#第一个答案instructions = first_answer.find('pre') or first_answer.find('code')#pre和code标签为目标代码块args['tags'] = [t.text for t in html('.post-tag')]if not instructions and not args['all']:text = first_answer.find('.post-text').eq(0).text()elif args['all']:texts = []for html_tag in first_answer.items('.post-text > *'):current_text = html_tag.text()if current_text:if html_tag[0].tag in ['pre', 'code']:texts.append(_format_output(current_text, args))else:texts.append(current_text)texts.append('\n---\nAnswer from {0}'.format(link))text = '\n'.join(texts)else:text = _format_output(instructions.eq(0).text(), args)if text is None:text = NO_ANSWER_MSGtext = text.strip()return textdef _get_instructions(args):links = _get_links(args['query'])if not links:return Falseanswers = []append_header = args['num_answers'] > 1initial_position = args['pos']for answer_number in range(args['num_answers']):current_position = answer_number + initial_positionargs['pos'] = current_positionanswer = _get_answer(args, links)if not answer:continueif append_header:answer = ANSWER_HEADER.format(current_position, answer)answer += '\n'answers.append(answer)return '\n'.join(answers)#启动缓存
def _enable_cache():if not os.path.exists(CACHE_DIR):os.makedirs(CACHE_DIR)requests_cache.install_cache(CACHE_FILE)#清除缓存
def _clear_cache():for cache in glob.glob('{0}*'.format(CACHE_FILE)):os.remove(cache)# 脚本主函数
def howdoi(args):#构造查询（主要是把问号删除）args['query'] = ' '.join(args['query']).replace('?', '')try:return _get_instructions(args) or 'Sorry, couldn\'t find any help with that topic\n'except (ConnectionError, SSLError):return 'Failed to establish network connection\n'#获取用户输入的命令行参数
def get_parser():parser = argparse.ArgumentParser(description='instant coding answers via the command line')parser.add_argument('query', metavar='QUERY', type=str, nargs='*',help='the question to answer')parser.add_argument('-p', '--pos', help='select answer in specified position (default: 1)', default=1, type=int)parser.add_argument('-a', '--all', help='display the full text of the answer',action='store_true')parser.add_argument('-l', '--link', help='display only the answer link',action='store_true')parser.add_argument('-c', '--color', help='enable colorized output',action='store_true')parser.add_argument('-n', '--num-answers', help='number of answers to return', default=1, type=int)parser.add_argument('-C', '--clear-cache', help='clear the cache',action='store_true')parser.add_argument('-v', '--version', help='displays the current version of howdoi',action='store_true')return parser#启动函数
def command_line_runner():parser = get_parser()args = vars(parser.parse_args())# 输出脚本版本if args['version']:print(__version__)return# 清除缓存if args['clear_cache']:_clear_cache()print('Cache cleared successfully')return# 如果没有query，就输出帮助信息if not args['query']:parser.print_help()return# 如果环境变量设置了禁止缓存，就清除缓存if not os.getenv('HOWDOI_DISABLE_CACHE'):_enable_cache()# 彩色输出if os.getenv('HOWDOI_COLORIZE'):args['color'] = True# 如果用户Python版本小于3就进行utf-8编码，如否，就正常启动if sys.version < '3':print(howdoi(args).encode('utf-8', 'ignore'))else:print(howdoi(args))if __name__ == '__main__':command_line_runner()