爬虫--下载网站存储（MongoDB）

该爬虫目的是下载网站页面并保存到MongoDB数据库，爬虫原型是《Web Scraping with Python》一书的第一章、第三章的代码，原代码是python2编写的，这里改用python3编写，在此基础上做一些恰当修改，补全爬虫完整，增强容错能力，支持robots检查、代理、限速、爬取深度设置。

from urllib.request import urlopen, URLError, HTTPError, Request, build_opener, ProxyHandler
from urllib.parse import urlparse, urljoin
from urllib.robotparser import RobotFileParser
from datetime import datetime, timedelta
import time
import random
import re
from pymongo import MongoClient

# 数据库存储
class MongoCache:
    def __init__(self, client=None, expires=timedelta(days=30)):
        self.client = MongoClient('localhost', 27017) if client is None else client
        self.db = self.client.cache
        self.db.webpage.create_index('timestamp', expireAfterSeconds=expires.total_seconds())

    def __getitem__(self, url):
        record = self.db.webpage.find_one({'_id': url})
        if record:
            return record['result']
        else:
            raise KeyError(f'{url} does not exist')

    def __setitem__(self, url, result):
        record = {'result': result, 'timestamp': datetime.now()}
        self.db.webpage.update({'_id': url}, {'$set': record}, upsert=True)

# 限速
class Throttle:
    def __init__(self, delay):
        self.delay = delay
        self.domains = {}

    def wait(self, url):
        domain = urlparse(url).netloc
        last_accessed = self.domains.get(domain)

        if self.delay > 0 and last_accessed is not None:
            sleep_secs = self.delay - (datetime.now() - last_accessed).seconds
            if sleep_secs > 0:
                time.sleep(sleep_secs)
        self.domains[domain] = datetime.now()

# 下载类，检查url是否已下载保存，否则下载保存
class Downloader:
    def __init__(self, delay=3, user_agent=None, proxies=None, num_retries=1, cache=None):
        self.throttle = Throttle(delay)
        self.user_agent = user_agent if user_agent else 'Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/66.0.3359.139 Safari/537.36'
        self.proxies = proxies
        self.num_retries = num_retries
        self.cache = cache

    def __call__(self, url):
        result = None
        if self.cache:
            try:
                result = self.cache[url]
            except KeyError:
                pass
            # else:
            #     if self.num_retries > 0 and 500 <= result['code'] < 600:
            #         result = None
        if result is None:
            self.throttle.wait(url)
            result = self.download(url, self.num_retries)
            if self.cache:
                self.cache[url] = result
        return result


    def download(self, url, num_retries):
        print('Downloading', url)
        headers = {'User-Agent': self.user_agent}
        proxy = random.choice(self.proxies) if self.proxies else None
        request = Request(url, headers=headers)
        opener = build_opener()
        if proxy:
            opener.add_handler(ProxyHandler({urlparse(url).scheme: proxy}))
        try:
            opened_web = opener.open(request)
            code = opened_web.code
            html = opened_web.read().decode()
        except (URLError, HTTPError, UnicodeDecodeError, UnicodeEncodeError) as e:
            print('Download error:', e.reason)
            html = None
            code = 0
            if num_retries > 0:
                if hasattr(e, 'code') and 500 <= e.code < 600:
                    return self.download(url, num_retries-1)
        return {'html': html, 'code': code}

def get_robots(rp, url):
    rp.set_url(urljoin(url, 'robots.txt'))
    rp.read()
    return rp

def get_link(html):
    webpage_regex = re.compile('<a[^>]+href=["\'](.*?)["\']', re.IGNORECASE)
    try:
        return webpage_regex.findall(html)
    except TypeError:
        return []

# 爬取链接，保存到link_save
# 第一个参数是要爬取的url，第二个参数是匹配链接的正则表达式，第三个参数是爬取的深度
def link_crawler(seed_url, link_regex, max_depth=2, cache=None):
    crawl_queue = [seed_url]
    link_save = {seed_url: 0}
    rp = RobotFileParser()
    robots_check = get_robots(rp, seed_url)
    downloader = Downloader(cache=cache)
    while crawl_queue:
        url = crawl_queue.pop()
        depth = link_save[url]
        if robots_check.can_fetch(downloader.user_agent, url):
            html = downloader(url)
            if depth <= max_depth:
                for link in get_link(html['html']):
                    # 相对链接使用这行代码合并绝对链接
                    # link = urljoin(seed_url, link)
                    if re.match(link_regex, link) and link not in link_save.keys():
                        crawl_queue.append(link)
                        link_save[link] = depth + 1
    # 完成所有任务后关闭数据库连接
    downloader.cache.client.close()


if __name__ == "__main__":
    link_crawler("http://cncarehk.com/", "http://cncarehk.com/.*?", cache=MongoCache(expires=timedelta(seconds=60)))