Python爬虫基础之requests

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一、随时随地爬取一个网页下来

  怎么爬取网页?对网站开发了解的都知道,浏览器访问Url向服务器发送请求,服务器响应浏览器请求并返回一堆HTML信息,其中包括html标签,css样式,js脚本等。我们之前用的是Python标准基础库Urllib实现的,

现在我们使用Python的Requests HTTP库写个脚本开始爬取网页。Requests的口号很响亮“让HTTP服务人类“,够霸气。

二、Python Requests库的基本使用

1.GET和POST请求方式

GET请求

1 import requests
2 
3 payload = {"t": "b", "w": "Python urllib"}
4 response = requests.get(http://zzk.cnblogs.com/s, params=payload)
5 # print(response.url)  # 打印 http://zzk.cnblogs.com/s?w=Python+urllib&t=b&AspxAutoDetectCookieSupport=1
6 print(response.text)  

Python requests的GET请求,不需要在作为请求参数前,对dict参数进行urlencode()和手动拼接到请求url后面,get()方法会直接对params参数这样做。

POST请求

1 import requests
2 
3 payload = {"t": "b", "w": "Python urllib"}
4 response = requests.post(http://zzk.cnblogs.com/s, data=payload)
5 print(response.text)  # u‘......‘

Python requests的POST请求,不需要在作为请求参数前,对dict参数进行urlencode()和encode()将字符串转换成字节码。raw属性返回的是字节码,text属性直接返回unicode格式的字符串,而不需要再进行decode()将返回的bytes字节码转化为unicode。

相对于Python urllib而言,Python requests更加简单易用。

 2.设置请求头headers

1 import requests
2 
3 payload = {"t": "b", "w": "Python urllib"}
4 headers = {user_agent:Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.36}
5 response = requests.get(http://zzk.cnblogs.com/s, params=payload, headers=headers)
6 print(response.request.headers)  

get方法的请求头,可以通过传递字典格式的参数给headers来实现。response.headers返回服务器响应的请求头信息,response.request.headers返回客户端的请求头信息。

3.设置会话cookie

1 import requests
2 
3 cookies = {cookies_are: working}
4 response = requests.get(http://zzk.cnblogs.com/, cookies=cookies)
5 print(response.text)

requests.get()方法cookies参数除了支持dict()字典格式,还支持传递一个复杂的RequestsCookieJar对象,可以指定域名和路径属性。

1 import requests
2 import requests.cookies
3 
4 cookieJar = requests.cookies.RequestsCookieJar()
5 cookieJar.set(cookies_are, working, domain=cnblogs, path=/cookies)
6 response = requests.get(http://zzk.cnblogs.com/, cookies=cookieJar)
7 print(response.text)

4.设置超时时间timeout

1 import requests
2 
3 response = requests.get(http://zzk.cnblogs.com/, timeout=0.001)
4 print(response.text)

 

三、Python Requests库的高级使用

1.Session Object

1 from requests import Request,Session
2 
3 s = Session()
4 
5 s.get(http://httpbin.org/cookies/set/sessioncookie/123456789)
6 r = s.get(http://httpbin.org/cookies)
7 
8 print(r.text)
9 # ‘{"cookies": {"sessioncookie": "123456789"}}‘

通过Session,我们可以在多个请求之间传递cookies信息,不过仅限于同一域名下,否则不会附带上cookie。如果碰到需要登录态的页面,我们可以在登陆的时候保存登录态,再访问其他页面时附带上就好。

2.Prepared Requested

 1 from requests import Request,Session
 2 
 3 url = http://zzk.cnblogs.com/s
 4 payload = {"t": "b", "w": "Python urllib"}
 5 headers = {
 6         user-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.36,
 7         Content-Type:application/x-www-form-urlencoded
 8 }
 9 s = Session()
10 request = Request(GET, url, headers=headers, data=payload)
11 prepped = request.prepare()
12 
13 # do something with prepped.headers
14 del prepped.headers[Content-Type]
15 response = s.send(prepped, timeout=3)
16 print(response.request.headers)

Request对象的prepare()方法返回的对象允许在发送请求前做些额外的工作,例如更新请求体body或者请求头headers.

四、Python Requests库的实际应用

 1.GET请求封装

 1 def do_get_request(self, url, headers=None, timeout=3, is_return_text=True, num_retries=2):
 2         if url is None:
 3             return None
 4         print(Downloading:, url)
 5         if headers is None:  # 默认请求头
 6             headers = {
 7                 user-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.36}
 8         response = None
 9         try:
10             response = requests.get(url,headers=headers,timeout=timeout)
11 
12             response.raise_for_status()  # a 4XX client error or 5XX server error response,raise requests.exceptions.HTTPError
13             if response.status_code == requests.codes.ok:
14                 if is_return_text:
15                     html = response.text
16                 else:
17                     html = response.json()
18             else:
19                 html = None
20         except requests.Timeout as err:
21             print(Downloading Timeout:, err.args)
22             html = None
23         except requests.HTTPError as err:
24             print(Downloading HTTP Error,msg:{0}.format(err.args))
25             html = None
26             if num_retries > 0:
27                 if 500 <= response.status_code < 600:
28                     return self.do_get_request(url, headers=headers, num_retries=num_retries - 1)  # 服务器错误,导致请求失败,默认重试2次
29         except requests.ConnectionError as err:
30             print(Downloading Connection Error:, err.args)
31             html = None
32 
33         return html

2.POST请求封装

 1  def do_post_request(self, url, data=None, headers=None, timeout=3, is_return_text=True, num_retries=2):
 2         if url is None:
 3             return None
 4         print(Downloading:, url)
 5         # 如果请求数据未空,直接返回
 6         if data is None:
 7             return
 8         if headers is None:
 9             headers = {
10                 user-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.36}
11         response = None
12         try:
13             response = requests.post(url,data=data, headers=headers, timeout=timeout)   # 设置headers timeout无效
14 
15             response.raise_for_status()  # a 4XX client error or 5XX server error response,raise requests.exceptions.HTTPError
16             if response.status_code == requests.codes.ok:
17                 if is_return_text:
18                     html = response.text
19                 else:
20                     html = response.json()
21             else:
22                 print(else)
23                 html = None
24         except requests.Timeout as err:
25             print(Downloading Timeout:, err.args)
26             html = None
27         except requests.HTTPError as err:
28             print(Downloading HTTP Error,msg:{0}.format(err.args))
29             html = None,
30             if num_retries > 0:
31                 if 500 <= response.status_code < 600:
32                     return self.do_post_request(url, data=data, headers=headers,
33                                                 num_retries=num_retries - 1)  # 服务器错误,导致请求失败,默认重试2次
34         except requests.ConnectionError as err:
35             print(Downloading Connection Error:, err.args)
36             html = None
37 
38         return html

3.登录态cookie

 1 def save_cookies(self, requeste_cookiejar, filename):
 2     with open(filename, wb)as f:
 3         pickle.dump(requeste_cookiejar, f)
 4 
 5 def load_cookies(self, filename):
 6     with open(filename, rb) as f:
 7         return pickle.load(f)
 8 
 9 # save request cookies
10 r = requests.get(url)
11 save_cookies(r.cookies,filename)
12 
13 # load cookies and do a request
14 requests.get(url,cookies=load_cookies(filename))

 

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