Python模块-requests(一)

requests不是python自带的，使用前需要安装

• 发送请求

HTTP请求类型有GET，POST，PUT，DELETE，HEAD和OPTIONS

使用requests发送请求的方法如下：

>>> import requests
>>> r = requests.get("http://httpbin.org/get") #发送GET请求
>>> r = requests.post("http://httpbin.org/post") #发送POST请求
>>> r = requests.put("http://httpbin.org/put") #发送PUT请求
>>> r = requests.delete("http://httpbin.org/delete") #发送DELETE请求
>>> r = requests.head("http://httpbin.org/get") #发送HEAD请求
>>> r = requests.options("http://httpbin.org/get") #发送OPTIONS请求

• 传递URL参数

params参数会对传入的参数进行拼接处理

通常使用params传的参数为字典的格式

>>> import requests
>>> payload = {"word":"test","page":11}
>>> r = requests.get("http://httpbin.org/get", params=payload)
>>> print(r.url) #打印r里的url参数的值
http://httpbin.org/get?word=test&page=11

字典里的值还可以是列表

>>> payload = {"word":"test","page":[1,2,3]}
>>> r = requests.get("http://httpbin.org/get", params=payload)
>>> print(r.url)
http://httpbin.org/get?word=test&page=1&page=2&page=3

字典中的值为None的键将不会被传参数到url里

>>> payload = {"word":"test","page":None}
>>> r = requests.get("http://httpbin.org/get", params=payload)
>>> print(r.url)
http://httpbin.org/get?word=test

params传的参数也可以直接是字符串

>>> payload = "word=test&page=11"
>>> r = requests.get("http://httpbin.org/get", params=payload)
>>> print(r.url)
http://httpbin.org/get?word=test&page=11

• 响应内容

requests能读取服务器响应的内容

>>> r = requests.get("https://www.cnblogs.com/")
>>> r.text #获取网页源代码
'''此处为网页源代码'''
>>> r.encoding #查看网页源代码的编码
'utf-8'
>>> r.encoding = 'GBK' #把网页源码的编码改为gbk
>>> r.encoding #再调用的时候，发现网页编码变成了gbk了
'GBK'

• 二进制响应内容

对于非文本请求，requests也能用字节的方式来访问请求响应体

>>> r = requests.get("http://p1.ifengimg.com/a/2018_06/75880eeacd0823d_size11_w230_h152.jpg")
>>> r.content
'''此处为bytes类型的图片内容'''
>>> r.text
'''一堆乱码'''

该方式也能用于文本请求，不过返回的结果为bytes类型

>>> r = requests.get("https://www.cnblogs.com/")
>>> r.text
'''此处为文本类型的网页源代码'''
>>> r.content
'''此处为bytes类型的网页源代码'''

• JSON响应内容

requests中也有一个内置的json解码器，帮助我们处理json数据

>>> import requests
>>> r = requests.get("https://github.com/timeline.json")
>>> r.json()
{'message': 'Hello there, wayfaring stranger. If you’re reading this then you probably didn’t see our blog post a couple of years back announcing that this API would go away: http://git.io/17AROg Fear not, you should be able to get what you need from the shiny new Events API instead.', 'documentation_url': 'https://developer.github.com/v3/activity/events/#list-public-events'}
>>> r.status_code
410
>>> r.raise_for_status
<bound method Response.raise_for_status of <Response [410]>>

如果json数据解码失败，就会抛出一个ValueError: No JSON object could be decoded的异常

但是成功调用r.json()也不能说明响应成功，有的服务器会在失败的响应中包含一个json对象，如HTTP 500的错误细节，这种json也会被解码返回

所以要检查请求是否成功，可以使用r.status_code和r.raise_for_status来检查

• 原始响应内容

requests获取来自服务器的原始套接字响应

>>> import requests
>>> r = requests.get("http://httpbin.org/get", stream=True)
>>> r.raw
<urllib3.response.HTTPResponse object at 0x000001B93F230518>
>>> r.raw.read(300)
b', \n    "Accept-Encoding": "gzip, deflate", \n    "Connection": "close", \n    "Host": "httpbin.org", \n    "User-Agent": "python-requests/2.18.4"\n  }, \n  "origin": "110.90.39.155", \n  "url": "http://httpbin.org/get"\n}\n'

要在初始请求中设置stream=True，然后用r.raw，可以使用r.raw.read()对内容进行读取

• 定制请求头

HTTP请求头为字典格式

>>> headers = {"user-agent":"Mozilla/5.0 (Windows NT 6.3; rv:36.0) Gecko/20100101 Firefox/36.0"}
>>> r = requests.get("http://httpbin.org/get",headers=headers)

定制的请求头的优先级低于某些特定的信息源，例如：

1. 如果在 .netrc 中设置了用户认证信息，使用请求头设置的授权就不会生效，而如果设置了 auth= 参数，.netrc 的设置就无效了
2. 如果被重定向到别的主机，授权的请求头就会被删除
3. 代理授权请求头会被URL中提供的代理身份覆盖掉
4. 在我们能判断内容长度的情况下，请求头的Content-Length会被改写

requests不会因为定制的请求头的具体情况改变自己的行为

只不过会在最后的请求中，所有的请求头信息都会被传递进去

所有的请求头值必须是 string、bytestring 或者 unicode

尽管传递 unicode header 也是允许的，但不建议这样做

• POST请求

想要给网站发送post数据，例如登陆某网站的时候，可以用requests发送post请求并发送数据

要发送的数据可以传data参数，然后使用post请求进行发送

发送的数据常为字典

>>> payload = "test" #post的数据为字符串
>>> r = requests.post("http://httpbin.org/post", data=payload)
>>> print(r.text)
{
  "args": {},
  "data": "test",
  "files": {},
  "form": {},
  "headers": {
    "Accept": "*/*",
    "Accept-Encoding": "gzip, deflate",
    "Connection": "close",
    "Content-Length": "4",
    "Host": "httpbin.org",
    "User-Agent": "python-requests/2.18.4"
  },
  "json": null,
  "origin": "110.90.39.155",
  "url": "http://httpbin.org/post"
}

>>> payload = {'username':'test','password':'test1234'} #post的数据为字典
>>> r = requests.post("http://httpbin.org/post", data=payload)
>>> print(r.text)
{
  "args": {},
  "data": "",
  "files": {},
  "form": {
    "password": "test1234",
    "username": "test"
  },
  "headers": {
    "Accept": "*/*",
    "Accept-Encoding": "gzip, deflate",
    "Connection": "close",
    "Content-Length": "31",
    "Content-Type": "application/x-www-form-urlencoded",
    "Host": "httpbin.org",
    "User-Agent": "python-requests/2.18.4"
  },
  "json": null,
  "origin": "110.90.39.155",
  "url": "http://httpbin.org/post"
}

>>> payload = {'username':['test','test123'],'password':'test1234'} #post的数据为字典和列表
>>> r = requests.post("http://httpbin.org/post", data=payload)
>>> print(r.text)
{
  "args": {},
  "data": "",
  "files": {},
  "form": {
    "password": "test1234",
    "username": [
      "test",
      "test123"
    ]
  },
  "headers": {
    "Accept": "*/*",
    "Accept-Encoding": "gzip, deflate",
    "Connection": "close",
    "Content-Length": "48",
    "Content-Type": "application/x-www-form-urlencoded",
    "Host": "httpbin.org",
    "User-Agent": "python-requests/2.18.4"
  },
  "json": null,
  "origin": "110.90.39.155",
  "url": "http://httpbin.org/post"
}

• POST请求发送文件

post请求不仅可以发送数据，也可以发送二进制文件，参数为file=二进制文件

>>> import requests
>>> files = {'file': open('python.txt', 'rb')} #以二进制打开
>>> r = requests.post('http://httpbin.org/post', files=files)
>>> print(r.text)
{
  "args": {},
  "data": "",
  "files": {
    "file": "Python\n" #文件的内容
  },
  "form": {},
  "headers": {
    "Accept": "*/*",
    "Accept-Encoding": "gzip, deflate",
    "Connection": "close",
    "Content-Length": "153",
    "Content-Type": "multipart/form-data; boundary=03080f2f96834a78b2d509d2741ff17a",
    "Host": "httpbin.org",
    "User-Agent": "python-requests/2.9.1"
  },
  "json": null,
  "origin": "110.90.39.155",
  "url": "http://httpbin.org/post"
}

• 响应状态码

可以检测响应状态码

>>> r = requests.get('http://httpbin.org/get')
>>> r.status_code
200
>>> r.status_code == requests.codes.ok #判断状态码是否为200
True

如果发送了一个错误的请求(4XX客户端错误，5XX服务器错误响应)，我们可以使用raise_for_status()来抛出异常

>>> r = requests.get('http://httpbin.org/status/404')
>>> r.status_code
404
>>> r.raise_for_status
<bound method Response.raise_for_status of <Response [404]>>
>>> r.raise_for_status()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\hp\AppData\Roaming\Python\Python36\site-packages\requests\models.py", line 935, in raise_for_status
    raise HTTPError(http_error_msg, response=self)
requests.exceptions.HTTPError: 404 Client Error: NOT FOUND for url: http://httpbin.org/status/404

如果状态码为200，raise_for_status()返回的None

• 响应头

获取一个请求的响应头

>>> r = requests.get('http://httpbin.org/get')
>>> r.headers
{
	'Connection': 'keep-alive',
	'Server': 'meinheld/0.6.1',
	'Date': 'Sun, 04 Feb 2018 10:27:03 GMT',
	'Content-Type': 'application/json',
	'Access-Control-Allow-Origin': '*',
	'Access-Control-Allow-Credentials': 'true',
	'X-Powered-By': 'Flask',
	'X-Processed-Time': '0.000623941421509',
	'Content-Length': '266',
	'Via': '1.1 vegur'
}

获取请求头中特定的一些内容，如Content-Type和X-Powered-By

>>> r = requests.get('http://httpbin.org/get')
>>> r.headers.get("Content-Type")
'application/json'
>>> r.headers["Content-Type"]
'application/json'
>>> r.headers.get("X-Powered-By")
'Flask'
>>> r.headers["X-Powered-By"]
'Flask'

就是根据字典的键获取对应的值

• COOKIE

如果响应中包含cookie，我们可以快速地访问他们

>>> r = requests.get("http://httpbin.org/get")
>>> r.cookies['example_cookie_name']
'example_cookie_value'

如果要发送cookies给网站，可以使用cookies参数

>>> cookies = {'uesrname':'test','password':'test1234'}
>>> r = requests.get('http://httpbin.org/cookies',cookies=cookies)
>>> print(r.text)
{
  "cookies": {
    "password": "test1234",
    "uesrname": "test"
  }
}

cookie返回的对象为RequestsCookieJar，它的行为和字典类似，但界面更为完整，适合跨域名跨路径使用。还可以把 Cookie Jar 传到 Requests 中

>>> jar = requests.cookies.RequestsCookieJar()
>>> jar.set('tasty_cookie', 'yum', domain='httpbin.org', path='/cookies')
>>> jar.set('gross_cookie', 'blech', domain='httpbin.org', path='/elsewhere')
>>> url = 'http://httpbin.org/cookies'
>>> r = requests.get(url, cookies=jar)
>>> r.text
'{"cookies": {"tasty_cookie": "yum"}}'

• 重定向与请求历史

默认情况下，除了HEAD请求，requests会处理所有的重定向请求

可以使用响应对象的history方法来追踪重定向

>>> r = requests.get('https://www.baidu.com/test.php')
>>> r.status_code
200
>>> r.url
'http://www.baidu.com/forbiddenip/forbidden.html'
>>> r.history
[<Response [302]>]

如果使用的请求方式为GET，POST，PUT，OPTIONS，PATCH，DELETE时，可以通过allow_redirects参数禁用重定向处理

>>> r = requests.get('https://www.baidu.com/test.php',allow_redirects=False)
>>> r.status_code
302
>>> r.url
'https://www.baidu.com/test.php'
>>> r.history
[]

如果HEAD请求方法需要重定向，也可以通过allow_redirects参数来进行重定向

• 超时

requests会在time参数设置的秒数过后停止等待响应

如果不使用，程序可能会永远失去响应

>>> requests.get('https://www.baidu.com', timeout=0.01)
'''省略一大堆'''
requests.exceptions.ConnectTimeout: HTTPSConnectionPool(host='www.baidu.com', port=443): Max retries exceeded with url: / (Caused by ConnectTimeoutError(<urllib3.connection.VerifiedHTTPSConnection object at 0x000001B93F2C3D68>, 'Connection to www.baidu.com timed out. (connect timeout=0.01)'))

timeout也能对读取时间进行设置

>>> requests.get('https://www.baidu.com', timeout=(5,1))

响应的时间为5秒，读取的时间为1秒

• 错误与异常

遇到网络问题（如：DNS 查询失败、拒绝连接等）时，Requests 会抛出一个 ConnectionError 异常

如果 HTTP 请求返回了不成功的状态码， Response.raise_for_status() 会抛出一个 HTTPError 异常

若请求超时，则抛出一个 Timeout 异常

若请求超过了设定的最大重定向次数，则会抛出一个 TooManyRedirects 异常

所有Requests显式抛出的异常都继承自 requests.exceptions.RequestException