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python網(wǎng)絡(luò)爬蟲步驟是什么
python網(wǎng)絡(luò)爬蟲步驟：首先準(zhǔn)備所需庫，編寫爬蟲調(diào)度程序；然后編寫url管理器，并編寫網(wǎng)頁下載器；接著編寫網(wǎng)頁解析器；**后編寫網(wǎng)頁輸出器即可。KeK少兒編程網(wǎng)-https://www.pxcodes.com
KeK少兒編程網(wǎng)-https://www.pxcodes.com
本教程操作環(huán)境：windows7系統(tǒng)、python3.9版，DELL G3電腦。KeK少兒編程網(wǎng)-https://www.pxcodes.com
python網(wǎng)絡(luò)爬蟲步驟KeK少兒編程網(wǎng)-https://www.pxcodes.com
（1）準(zhǔn)備所需庫KeK少兒編程網(wǎng)-https://www.pxcodes.com
我們需要準(zhǔn)備一款名為BeautifulSoup（網(wǎng)頁解析）的開源庫，用于對下載的網(wǎng)頁進(jìn)行解析，我們是用的是PyCharm編譯環(huán)境所以可以直接下載該開源庫。KeK少兒編程網(wǎng)-https://www.pxcodes.com
步驟如下：KeK少兒編程網(wǎng)-https://www.pxcodes.com
選擇File->SettingsKeK少兒編程網(wǎng)-https://www.pxcodes.com
KeK少兒編程網(wǎng)-https://www.pxcodes.com
打開Project:PythonProject下的Project interpreterKeK少兒編程網(wǎng)-https://www.pxcodes.com
KeK少兒編程網(wǎng)-https://www.pxcodes.com
點擊加號添加新的庫KeK少兒編程網(wǎng)-https://www.pxcodes.com
KeK少兒編程網(wǎng)-https://www.pxcodes.com
輸入bs4選擇bs4點擊Install Packge進(jìn)行下載KeK少兒編程網(wǎng)-https://www.pxcodes.com
KeK少兒編程網(wǎng)-https://www.pxcodes.com
（2）編寫爬蟲調(diào)度程序KeK少兒編程網(wǎng)-https://www.pxcodes.com
這里的bike_spider是項目名稱引入的四個類分別對應(yīng)下面的四段代碼url管理器，url下載器，url解析器，url輸出器。KeK少兒編程網(wǎng)-https://www.pxcodes.com
# 爬蟲調(diào)度程序 from bike_spider import url_manager, html_downloader, html_parser, html_outputer # 爬蟲初始化 class SpiderMain(object): def __init__(self): self.urls = url_manager.UrlManager() self.downloader = html_downloader.HtmlDownloader() self.parser = html_parser.HtmlParser() self.outputer = html_outputer.HtmlOutputer() def craw(self, my_root_url): count = 1 self.urls.add_new_url(my_root_url) while self.urls.has_new_url(): try: new_url = self.urls.get_new_url() print("craw %d : %s" % (count, new_url)) # 下載網(wǎng)頁 html_cont = self.downloader.download(new_url) # 解析網(wǎng)頁 new_urls, new_data = self.parser.parse(new_url, html_cont) self.urls.add_new_urls(new_urls) # 網(wǎng)頁輸出器收集數(shù)據(jù) self.outputer.collect_data(new_data) if count == 10: break count += 1 except: print("craw failed") self.outputer.output_html() if __name__ == "__main__": root_url = "http://baike.baidu.com/item/Python/407313" obj_spider = SpiderMain() obj_spider.craw(root_url)(3)編寫url管理器KeK少兒編程網(wǎng)-https://www.pxcodes.com
我們把已經(jīng)爬取過的url和未爬取的url分開存放以便我們不會重復(fù)爬取某些已經(jīng)爬取過的網(wǎng)頁。KeK少兒編程網(wǎng)-https://www.pxcodes.com
# url管理器 class UrlManager(object): def __init__(self): self.new_urls = set() self.old_urls = set() def add_new_url(self, url): if url is None: return if url not in self.new_urls and url not in self.old_urls: self.new_urls.add(url) def add_new_urls(self, urls): if urls is None or len(urls) == 0: return for url in urls: self.new_urls.add(url) def get_new_url(self): # pop方法會幫我們獲取一個url并且移除它 new_url = self.new_urls.pop() self.old_urls.add(new_url) return new_url def has_new_url(self): return len(self.new_urls) != 0（4）編寫網(wǎng)頁下載器KeK少兒編程網(wǎng)-https://www.pxcodes.com
通過網(wǎng)絡(luò)請求來下載頁面KeK少兒編程網(wǎng)-https://www.pxcodes.com
# 網(wǎng)頁下載器 import urllib.request class HtmlDownloader(object): def download(self, url): if url is None: return None response = urllib.request.urlopen(url) # code不為200則請求失敗 if response.getcode() != 200: return None return response.read()（5）編寫網(wǎng)頁解析器KeK少兒編程網(wǎng)-https://www.pxcodes.com
對網(wǎng)頁進(jìn)行解析時我們需要知道我們要查詢的內(nèi)容都有哪些特征，我們可以打開一個網(wǎng)頁點擊右鍵審查元素來了解我們所查內(nèi)容的共同之處。KeK少兒編程網(wǎng)-https://www.pxcodes.com
# 網(wǎng)頁解析器 import re from bs4 import BeautifulSoup from urllib.parse import urljoin class HtmlParser(object): def parse(self, page_url, html_cont): if page_url is None or html_cont is None: return soup = BeautifulSoup(html_cont, "html.parser", from_encoding="utf-8") new_urls = self._get_new_urls(page_url, soup) new_data = self._get_new_data(page_url, soup) return new_urls, new_data def _get_new_data(self, page_url, soup): res_data = {"url": page_url} # 獲取標(biāo)題 title_node = soup.find("dd", class_="lemmaWgt-lemmaTitle-title").find("h1") res_data["title"] = title_node.get_text() summary_node = soup.find("p", class_="lemma-summary") res_data["summary"] = summary_node.get_text() return res_data def _get_new_urls(self, page_url, soup): new_urls = set() # 查找出所有符合下列條件的url links = soup.find_all("a", href=re.compile(r"/item/")) for link in links: new_url = link['href'] # 獲取到的url不完整，學(xué)要拼接 new_full_url = urljoin(page_url, new_url) new_urls.add(new_full_url) return new_urls（6）編寫網(wǎng)頁輸出器KeK少兒編程網(wǎng)-https://www.pxcodes.com
輸出的格式有很多種，我們選擇以html的形式輸出，這樣我們可以的到一個html頁面。KeK少兒編程網(wǎng)-https://www.pxcodes.com
# 網(wǎng)頁輸出器 class HtmlOutputer(object): def __init__(self): self.datas = [] def collect_data(self, data): if data is None: return self.datas.append(data) # 我們以html表格形式進(jìn)行輸出 def output_html(self): fout = open("output.html", "w", encoding='utf-8') fout.write("<html>") fout.write("<meta charset='utf-8'>") fout.write("<body>") # 以表格輸出 fout.write("<table>") for data in self.datas: # 一行 fout.write("<tr>") # 每個單元行的內(nèi)容 fout.write("<td>%s</td>" % data["url"]) fout.write("<td>%s</td>" % data["title"]) fout.write("<td>%s</td>" % data["summary"]) fout.write("</tr>") fout.write("</table>") fout.write("</body>") fout.write("</html>") # 輸出完畢后一定要關(guān)閉輸出器 fout.close()相關(guān)免費學(xué)習(xí)推薦：python視頻教程KeK少兒編程網(wǎng)-https://www.pxcodes.com
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