明天python视频教程栏目为各人引见Python的Spider (爬虫)相干常识。
1、网络爬虫
网络爬虫又被称为网络蜘蛛,咱们能够把互联网设想成一个蜘蛛网,每个网站都是一个节点,咱们能够应用一只蜘蛛去各个网页抓取咱们想要的资本。举一个最简略的例子,你正在baidu以及google中输出‘Python',会有年夜量以及Python相干的网页被检索进去,baidu以及google是若何从海量的网页中检索出你想要的资本,他们靠的就是派出年夜量蜘蛛去网页上爬取,检索要害字,建设索引数据库,通过复杂的排序算法,后果依照搜寻要害字相干度的高下展示给你。
千里之行,始于足下,咱们从最根底的开端学习若何写一个网络爬虫,完成言语应用Python。
2、Python若何拜访互联网
想要写网络爬虫,第一步是拜访互联网,Python若何拜访互联网呢?
正在Python中,咱们应用urllib包拜访互联网。(正在Python3中,对这个模块做了比拟年夜的调整,之前有urllib以及urllib2,正在3中对这两个模块做了对立兼并,称为urllib包。包上面蕴含了四个模块,urllib.request,urllib.error,urllib.parse,urllib.robotparser),今朝次要应用的是urllib.request。
咱们起首举一个最简略的例子,若何猎取猎取网页的源码:
import urllib.request response = urllib.request.urlopen('https://docs.python.org/3/') html = response.read()print(html.decode('utf-8'))
3、Python网络简略应用
起首咱们用两个小demo练一下手,一个是应用python代码下载一张图片到内陆,另外一个是挪用有道翻译写一个翻译小软件。
3.1依据图片链接下载图片,代码以下:
import urllib.request response = urllib.request.urlopen('http://www.3lian.com/e/ViewImg/index.html?url=http://img16.3lian.com/gif2016/w1/3/d/61.jpg') image = response.read() with open('123.jpg','wb') as f: f.write(image)
此中response是一个工具
输出:response.geturl()
->'http://www.3lian.com/e/ViewImg/index.html?url=http://img16.3lian.com/gif2016/w1/3/d/61.jpg'
输出:response.info()
-><http.client.HTTPMessage object at 0x10591c0b8>
输出:print(response.info())
->Content-Type: text/html
Last-Modified: Mon, 27 Sep 2004 01:23:20 GMT
Accept-Ranges: bytes
ETag: "0f4b59230a4c41:0"
Server: Microsoft-IIS/8.0
Date: Sun, 14 Aug 2016 07:16:01 GMT
Connection: close
Content-Length: 2827
输出:response.getcode()
->200
3.1应用有道辞书完成翻译性能
咱们想完成翻译性能,咱们需求拿到申请链接。起首咱们需求进入有道首页,点击翻译,正在翻译界面输出要翻译的内容,点击翻译按钮,就会向效劳器发动一个申请,咱们需求做的就是拿到申请地点以及申请参数。
我正在此应用google阅读器完成拿到申请地点以及申请参数。起首点击右键,点击反省(没有同阅读器点击的选项可能没有同,同一阅读器的没有同版本也可能没有同),进入图一所示,从中咱们能够拿到申请申请地点以及申请参数,正在Header中的Form Data中咱们能够拿到申请参数。
(图一)
代码段以下:
import urllib.requestimport urllib.parse url = 'http://fanyi.youdao.com/translate?smartresult=dict&smartresult=rule&smartresult=ugc&sessionFrom=dict2.index'data = {} data['type'] = 'AUTO'data['i'] = 'i love you'data['doctype'] = 'json'data['xmlVersion'] = '1.8'data['keyfrom'] = 'fanyi.web'data['ue'] = 'UTF-8'data['action'] = 'FY_BY_CLICKBUTTON'data['typoResult'] = 'true'data = urllib.parse.urlencode(data).encode('utf-8') response = urllib.request.urlopen(url,data) html = response.read().decode('utf-8')print(html)
上述代码执行以下:
{"type":"EN2ZH_CN","errorCode":0,"elapsedTime":0,"translateResult":[[{"src":"i love you","tgt":"我爱你"}]],"smartResult":{"type":1,"entries":["","我爱你。"]}}
关于上述后果,咱们能够看到是一个json串,咱们能够对此解析一下,而且对代码进行欠缺一下:
import urllib.requestimport urllib.parseimport json url = 'http://fanyi.youdao.com/translate?smartresult=dict&smartresult=rule&smartresult=ugc&sessionFrom=dict2.index'data = {} data['type'] = 'AUTO'data['i'] = 'i love you'data['doctype'] = 'json'data['xmlVersion'] = '1.8'data['keyfrom'] = 'fanyi.web'data['ue'] = 'UTF-8'data['action'] = 'FY_BY_CLICKBUTTON'data['typoResult'] = 'true'data = urllib.parse.urlencode(data).encode('utf-8') response = urllib.request.urlopen(url,data) html = response.read().decode('utf-8') target = json.loads(html)print(target['translateResult'][0][0]['tgt'])
4、躲避危险
效劳器检测出申请没有是来自阅读器,可能会屏蔽掉申请,效劳器判别的根据是应用‘User-Agent',咱们能够修正改字段的值,来暗藏本人。代码以下:
import urllib.requestimport urllib.parseimport json url = 'http://fanyi.youdao.com/translate?smartresult=dict&smartresult=rule&smartresult=ugc&sessionFrom=dict2.index'data = {} data['type'] = 'AUTO'data['i'] = 'i love you'data['doctype'] = 'json'data['xmlVersion'] = '1.8'data['keyfrom'] = 'fanyi.web'data['ue'] = 'UTF-8'data['action'] = 'FY_BY_CLICKBUTTON'data['typoResult'] = 'true'data = urllib.parse.urlencode(data).encode('utf-8') req = urllib.request.Request(url, data) req.add_header('User-Agent','Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_2) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/52.0.2743.116 Safari/537.36') response = urllib.request.urlopen(url, data) html = response.read().decode('utf-8') target = json.loads(html)print(target['translateResult'][0][0]['tgt'])
View Code
上述做法尽管能够暗藏本人,然而另有很年夜成绩,例如一个网络爬虫下载图片软件,正在短期内年夜量下载图片,效劳器能够能够依据IP拜访次数判别能否是失常拜访。一切上述做法另有很年夜的成绩。咱们能够经过两种做法处理方法,一是应用提早,例如5秒内拜访一次。另外一种方法是应用代办署理。
提早拜访(休眠5秒,缺陷是拜访效率低下):
import urllib.requestimport urllib.parseimport jsonimport timewhile True: content = input('please input content(input q exit program):') if content == 'q': break; url = 'http://fanyi.youdao.com/translate?smartresult=dict&smartresult=rule&smartresult=ugc&sessionFrom=dict2.index' data = {} data['type'] = 'AUTO' data['i'] = content data['doctype'] = 'json' data['xmlVersion'] = '1.8' data['keyfrom'] = 'fanyi.web' data['ue'] = 'UTF-8' data['action'] = 'FY_BY_CLICKBUTTON' data['typoResult'] = 'true' data = urllib.parse.urlencode(data).encode('utf-8') req = urllib.request.Request(url, data) req.add_header('User-Agent','Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_2) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/52.0.2743.116 Safari/537.36') response = urllib.request.urlopen(url, data) html = response.read().decode('utf-8') target = json.loads(html) print(target['translateResult'][0][0]['tgt']) time.sleep(5)
View Code
代办署理拜访:让代办署理拜访资本,而后讲拜访到的资本前往。效劳器看到的是代办署理的IP地点,没有是本人地点,效劳器就不方法对你做限度。
步骤:
1,参数是一个字典{'类型' : '代办署理IP:端标语' } //类型是http,https等
proxy_support = urllib.request.ProxyHandler({})
2,定制、创立一个opener
opener = urllib.request.build_opener(proxy_support)
3,装置opener(永世装置,一劳永逸)
urllib.request.install_opener(opener)
3,挪用opener(挪用的时分应用)
opener.open(url)
5、批量下载网络图片
图片下载起源为煎蛋网(http://jandan.net)
图片下载的要害是找到图片的法则,如找到以后页,每一一页的图片链接,而后应用轮回下载图片。上面是顺序代码(待优化,正则表白式婚配,IP代办署理):
import urllib.requestimport osdef url_open(url): req = urllib.request.Request(url) req.add_header('User-Agent','Mozilla/5.0') response = urllib.request.urlopen(req) html = response.read() return htmldef get_page(url): html = url_open(url).decode('utf-8') a = html.find('current-co妹妹ent-page') + 23 b = html.find(']',a) return html[a:b]def find_image(url): html = url_open(url).decode('utf-8') image_addrs = [] a = html.find('img src=') while a != -1: b = html.find('.jpg',a,a + 150) if b != -1: image_addrs.append(html[a+9:b+4]) else: b = a + 9 a = html.find('img src=',b) for each in image_addrs: print(each) return image_addrsdef save_image(folder,image_addrs): for each in image_addrs: filename = each.split('/')[-1] with open(filename,'wb') as f: img = url_open(each) f.write(img)def download_girls(folder = 'girlimage',pages = 20): os.mkdir(folder) os.chdir(folder) url = 'http://jandan.net/ooxx/' page_num = int(get_page(url)) for i in range(pages): page_num -= i page_url = url + 'page-' + str(page_num) + '#co妹妹ents' image_addrs = find_image(page_url) save_image(folder,image_addrs)if __name__ == '__main__': download_girls()
代码运转成果以下:
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