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
import requests
payload = {"t": "b", "w": "Python urllib"}
response = requests.get('http://zzk.cnblogs.com/s', params=payload)
# print(response.url) # 打印 http://zzk.cnblogs.com/s?w=Python+urllib&t=b&AspxAutoDetectCookieSupport=1
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
import requests
payload = {"t": "b", "w": "Python urllib"}
response = requests.post('http://zzk.cnblogs.com/s', data=payload)
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
import requests
payload = {"t": "b", "w": "Python urllib"}
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'}
response = requests.get('http://zzk.cnblogs.com/s', params=payload, headers=headers)
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
import requests
cookies = {'cookies_are': 'working'}
response = requests.get('http://zzk.cnblogs.com/', cookies=cookies)
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。
import requests
import requests.cookies cookieJar = requests.cookies.RequestsCookieJar()
cookieJar.set('cookies_are', 'working', domain='cnblogs', path='/cookies')
response = requests.get('http://zzk.cnblogs.com/', cookies=cookieJar)
print(response.text)
4.设置超时时间timeout
import requests
response = requests.get('http://zzk.cnblogs.com/', timeout=0.001)
print(response.text)
三、Python Requests库的高级使用
1.Session Object
from requests import Request,Session
s = Session()
s.get('http://httpbin.org/cookies/set/sessioncookie/123456789')
r = s.get('http://httpbin.org/cookies')
print(r.text)
# '{"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
from requests import Request,Session url = 'http://zzk.cnblogs.com/s'
payload = {"t": "b", "w": "Python urllib"}
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',
'Content-Type':'application/x-www-form-urlencoded'
}
s = Session()
request = Request('GET', url, headers=headers, data=payload)
prepped = request.prepare() # do something with prepped.headers
del prepped.headers['Content-Type']
response = s.send(prepped, timeout=3)
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.
3.Set Proxy
import requests # set headers
user_agent = 'Mozilla/5.0 (iPhone; CPU iPhone OS 8_0 like Mac OS X) AppleWebKit/600.1.3 (KHTML, like Gecko) Version/8.0 Mobile/12A4345d Safari/600.1.4'
headers = {'User-Agent': user_agent}
url = 'http://passport.xxx.com/auth/valid.json'
proxies = {'http': 'http://10.1.1.1:80'} # set http proxy
params = {'uin': 'xxxxxx', 'passwd': 'xxxxxx', 'imgcode': 'ijyk', '_1': '',
'_2': '', '_3': '', 'url': ''} response = requests.post(url, headers=headers, data=params, proxies=proxies)
response.raise_for_status()
if response.status_code == requests.codes.ok:
print(response.text)
requests.get()和post()方法均支持http proxy代理，只要传递proxies = {'http': 'http://10.1.1.1:80'}字典对象，可以实现把请求传递给代理服务器，代理服务器从10.1.1.1:80取回响应数据返回来。
四、Python Requests库的实际应用
1.GET请求封装
def do_get_request(self, url, headers=None, timeout=3, is_return_text=True, num_retries=2):
if url is None:
return None
print('Downloading:', url)
if headers is None: # 默认请求头
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'}
response = None
try:
response = requests.get(url,headers=headers,timeout=timeout) response.raise_for_status() # a 4XX client error or 5XX server error response,raise requests.exceptions.HTTPError
if response.status_code == requests.codes.ok:
if is_return_text:
html = response.text
else:
html = response.json()
else:
html = None
except requests.Timeout as err:
print('Downloading Timeout:', err.args)
html = None
except requests.HTTPError as err:
print('Downloading HTTP Error,msg:{0}'.format(err.args))
html = None
if num_retries > 0:
if 500 <= response.status_code < 600:
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
except requests.ConnectionError as err:
print('Downloading Connection Error:', err.args)
html = None return html
2.POST请求封装
def do_post_request(self, url, data=None, headers=None, timeout=3, is_return_text=True, num_retries=2):
if url is None:
return None
print('Downloading:', url)
# 如果请求数据未空，直接返回
if data is None:
return
if headers is None:
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'}
response = None
try:
response = requests.post(url,data=data, headers=headers, timeout=timeout) # 设置headers timeout无效 response.raise_for_status() # a 4XX client error or 5XX server error response,raise requests.exceptions.HTTPError
if response.status_code == requests.codes.ok:
if is_return_text:
html = response.text
else:
html = response.json()
else:
print('else')
html = None
except requests.Timeout as err:
print('Downloading Timeout:', err.args)
html = None
except requests.HTTPError as err:
print('Downloading HTTP Error,msg:{0}'.format(err.args))
html = None,
if num_retries > 0:
if 500 <= response.status_code < 600:
return self.do_post_request(url, data=data, headers=headers,
num_retries=num_retries - 1) # 服务器错误，导致请求失败，默认重试2次
except requests.ConnectionError as err:
print('Downloading Connection Error:', err.args)
html = None return html
3.登录态cookie
def save_cookies(self, requeste_cookiejar, filename):
with open(filename, 'wb')as f:
pickle.dump(requeste_cookiejar, f) def load_cookies(self, filename):
with open(filename, 'rb') as f:
return pickle.load(f) # save request cookies
r = requests.get(url)
save_cookies(r.cookies,filename) # load cookies and do a request
requests.get(url,cookies=load_cookies(filename))