Python Requests模块讲解4

高级用法

本篇文档涵盖了Requests的一些更加高级的特性。

会话对象

会话对象让你能够跨请求保持某些参数。它也会在同一个Session实例发出的所有请求之间保持cookies。

会话对象具有主要的Requests API的所有方法。

我们来跨请求保持一些cookies:

s = requests.Session() s.get('http://httpbin.org/cookies/set/sessioncookie/123456789') 
r = s.get("http://httpbin.org/cookies") 
print(r.text) 
# '{"cookies": {"sessioncookie": "123456789"}}'

会话也可用来为请求方法提供缺省数据。这是通过为会话对象的属性提供数据来实现的:

s = requests.Session() 
s.auth = ('user', 'pass') 
s.headers.update({'x-test': 'true'}) 
# both 'x-test' and 'x-test2' are sent s.get('http://httpbin.org/headers', headers={'x-test2': 'true'})

任何你传递给请求方法的字典都会与已设置会话层数据合并。方法层的参数覆盖会话的参数。

从字典参数中移除一个值

有时你会想省略字典参数中一些会话层的键。要做到这一点，你只需简单地在方法层参数中将那个键的值设置为 None ，那个键就会被自动省略掉。

包含在一个会话中的所有数据你都可以直接使用。学习更多细节请阅读 会话API文档 。

请求与响应对象

任何时候调用requests.*()你都在做两件主要的事情。其一，你在构建一个 Request 对象， 该对象将被发送到某个服务器请求或查询一些资源。其二，一旦 requests 得到一个从 服务器返回的响应就会产生一个 Response 对象。该响应对象包含服务器返回的所有信息， 也包含你原来创建的 Request 对象。如下是一个简单的请求，从Wikipedia的服务器得到 一些非常重要的信息:

>>> r = requests.get('http://en.wikipedia.org/wiki/Monty_Python')

如果想访问服务器返回给我们的响应头部信息，可以这样做:

>>> r.headers 
{'content-length': '56170', 'x-content-type-options': 'nosniff', 'x-cache': 'HIT from cp1006.eqiad.wmnet, MISS from cp1010.eqiad.wmnet', 'content-encoding': 'gzip', 'age': '3080', 'content-language': 'en', 'vary': 'Accept-Encoding,Cookie', 'server': 'Apache', 'last-modified': 'Wed, 13 Jun 2012 01:33:50 GMT', 'connection': 'close', 'cache-control': 'private, s-maxage=0, max-age=0, must-revalidate', 'date': 'Thu, 14 Jun 2012 12:59:39 GMT', 'content-type': 'text/html; charset=UTF-8', 'x-cache-lookup': 'HIT from cp1006.eqiad.wmnet:3128, MISS from cp1010.eqiad.wmnet:80'}

然而，如果想得到发送到服务器的请求的头部，我们可以简单地访问该请求，然后是该请求的头部:

>>> r.request.headers 
{'Accept-Encoding': 'identity, deflate, compress, gzip', 'Accept': '*/*', 'User-Agent': 'python-requests/0.13.1'}

Prepared Requests

Whenever you receive a Response object from an API call or a Session call, therequest attribute is actually the PreparedRequest that was used. In some cases you may wish to do some extra work to the body or headers (or anything else really) before sending a request. The simple recipe for this is the following:

from requests import Request, Session 
s = Session() 
req = Request('GET', url, data=data, headers=header ) 
prepped = req.prepare() 
# do something with prepped.body 
# do something with prepped.headers 
resp = s.send(prepped, stream=stream, verify=verify, proxies=proxies, cert=cert, timeout=timeout ) 
print(resp.status_code)

Since you are not doing anything special with the Request object, you prepare it immediately and modify the PreparedRequest object. You then send that with the other parameters you would have sent to requests.* or Session.*.

However, the above code will lose some of the advantages of having a RequestsSession object. In particular, Session-level state such as cookies will not get applied to your request. To get a PreparedRequest with that state applied, replace the call toRequest.prepare() with a call to Session.prepare_request(), like this:

from requests import Request, Session

s = Session()
req = Request('GET',  url,
    data=data
    headers=headers
)

prepped = s.prepare_request(req)

# do something with prepped.body
# do something with prepped.headers

resp = s.send(prepped,
    stream=stream,
    verify=verify,
    proxies=proxies,
    cert=cert,
    timeout=timeout
)

print(resp.status_code)

SSL证书验证

Requests可以为HTTPS请求验证SSL证书，就像web浏览器一样。要想检查某个主机的SSL证书，你可以使用 verify 参数:

>>> requests.get('https://kennethreitz.com', verify=True) 
requests.exceptions.SSLError: hostname 'kennethreitz.com' doesn't match either of '*.herokuapp.com', 'herokuapp.com'

在该域名上我没有设置SSL，所以失败了。但Github设置了SSL:

>>> requests.get('https://github.com', verify=True) 
<Response [200]>

对于私有证书，你也可以传递一个CA_BUNDLE文件的路径给 verify 。你也可以设置REQUEST_CA_BUNDLE 环境变量。

如果你将 verify 设置为False，Requests也能忽略对SSL证书的验证。

>>> requests.get('https://kennethreitz.com', verify=False) 
<Response [200]>

默认情况下， verify 是设置为True的。选项 verify 仅应用于主机证书。

你也可以指定一个本地证书用作客户端证书，可以是单个文件（包含密钥和证书）或一个包含两个文件路径的元组:

>>> requests.get('https://kennethreitz.com', cert=('/path/server.crt', '/path/key'))
 <Response [200]>

如果你指定了一个错误路径或一个无效的证书:

>>> requests.get('https://kennethreitz.com', cert='/wrong_path/server.pem') 
SSLError: [Errno 336265225] _ssl.c:347: error:140B0009:SSL routines:SSL_CTX_use_PrivateKey_file:PEM lib

响应体内容工作流

默认情况下，当你进行网络请求后，响应体会立即被下载。你可以通过 stream 参数覆盖这个行为，推迟下载响应体直到访问 Response.content 属性:

tarball_url = 'https://github.com/kennethreitz/requests/tarball/master' 
r = requests.get(tarball_url, stream=True)

此时仅有响应头被下载下来了，连接保持打开状态，因此允许我们根据条件获取内容:

if int(r.headers['content-length'])
< TOO_LONG: content = r.content ...

你可以进一步使用 Response.iter_content 和 Response.iter_lines 方法来控制工作流，或者以 Response.raw 从底层urllib3的 urllib3.HTTPResponse<urllib3.response.HTTPResponse 读取。

If you set stream to True when making a request, Requests cannot release the connection back to the pool unless you consume all the data or call Response.close. This can lead to inefficiency with connections. If you find yourself partially reading request bodies (or not reading them at all) while using stream=True, you should consider using contextlib.closing (documented here), like this:

from contextlib import closing

with closing(requests.get('http://httpbin.org/get', stream=True)) as r:
    # Do things with the response here.

保持活动状态（持久连接）

好消息 - 归功于urllib3，同一会话内的持久连接是完全自动处理的！同一会话内你发出的任何请求都会自动复用恰当的连接！

注意：只有所有的响应体数据被读取完毕连接才会被释放为连接池；所以确保将 stream设置为 False 或读取 Response 对象的 content 属性。

流式上传

Requests支持流式上传，这允许你发送大的数据流或文件而无需先把它们读入内存。要使用流式上传，仅需为你的请求体提供一个类文件对象即可:

with open('massive-body') as f: 
    requests.post('http://some.url/streamed', data=f)

块编码请求

对于出去和进来的请求，Requests也支持分块传输编码。要发送一个块编码的请求，仅需为你的请求体提供一个生成器（或任意没有具体长度(without a length)的迭代器）:

def gen(): 
    yield 'hi' 
    yield 'there' 
requests.post('http://some.url/chunked', data=gen())

POST Multiple Multipart-Encoded Files

You can send multiple files in one request. For example, suppose you want to upload image files to an HTML form with a multiple file field ‘images’:

<input type=”file” name=”images” multiple=”true” required=”true”/>

To do that, just set files to a list of tuples of (form_field_name, file_info):

>>> url = 'http://httpbin.org/post' 
>>> multiple_files = [('images', ('foo.png', open('foo.png', 'rb'), 'image/png')),  ('images', ('bar.png', open('bar.png', 'rb'), 'image/png'))] 
>>> r = requests.post(url, files=multiple_files) 
>>> r.text 
{  ...  'files': {'images': 'data:image/png;base64,iVBORw ....'}  'Content-Type': 'multipart/form-data; boundary=3131623adb2043caaeb5538cc7aa0b3a',  ... }

事件挂钩

Requests有一个钩子系统，你可以用来操控部分请求过程，或信号事件处理。

可用的钩子:

response:

从一个请求产生的响应

你可以通过传递一个 {hook_name: callback_function} 字典给 hooks 请求参数 为每个请求分配一个钩子函数:

hooks=dict(response=print_url)

callback_function 会接受一个数据块作为它的第一个参数。

def print_url(r): print(r.url)

若执行你的回调函数期间发生错误，系统会给出一个警告。

若回调函数返回一个值，默认以该值替换传进来的数据。若函数未返回任何东西， 也没有什么其他的影响。

我们来在运行期间打印一些请求方法的参数:

>>> requests.get('http://httpbin.org', hooks=dict(response=print_url)) 
http://httpbin.org 
<Response [200]>

自定义身份验证

Requests允许你使用自己指定的身份验证机制。

任何传递给请求方法的 auth 参数的可调用对象，在请求发出之前都有机会修改请求。

自定义的身份验证机制是作为 requests.auth.AuthBase 的子类来实现的，也非常容易定义。

Requests在 requests.auth 中提供了两种常见的的身份验证方案： HTTPBasicAuth 和HTTPDigestAuth 。

假设我们有一个web服务，仅在 X-Pizza 头被设置为一个密码值的情况下才会有响应。虽然这不太可能， 但就以它为例好了

from requests.auth import AuthBase 
class PizzaAuth(AuthBase): 
"""Attaches HTTP Pizza Authentication to the given Request object.""" 
   def __init__(self, username): 
      # setup any auth-related data here 
      self.username = username 
   def __call__(self, r): 
      # modify and return the request 
      r.headers['X-Pizza'] = self.username 
      return r

然后就可以使用我们的PizzaAuth来进行网络请求:

>>> requests.get('http://pizzabin.org/admin', auth=PizzaAuth('kenneth')) 
<Response [200]>

流式请求

使用 requests.Response.iter_lines() 你可以很方便地对流式API（例如 Twitter的流式API ）进行迭代。简单地设置 stream 为 True 便可以使用 iter_lines() 对相应进行迭代:

import json 
import requests 

r = requests.get('http://httpbin.org/stream/20', stream=True) 
for line in r.iter_lines(): 
   # filter out keep-alive new lines 
   if line: 
      print(json.loads(line))

代理

如果需要使用代理，你可以通过为任意请求方法提供 proxies 参数来配置单个请求:

import requests 
proxies = { "http": "http://10.10.1.10:3128", "https": "http://10.10.1.10:1080", } 
requests.get("http://example.org", proxies=proxies)

你也可以通过环境变量 HTTP_PROXY 和 HTTPS_PROXY 来配置代理。

$ export HTTP_PROXY="http://10.10.1.10:3128"
$ export HTTPS_PROXY="http://10.10.1.10:1080"
$ python
>>> import requests
>>> requests.get("http://example.org")

若你的代理需要使用HTTP Basic Auth，可以使用 http://user:password@host/ 语法:

proxies = { "http": "http://user:[email protected]:3128/", }

合规性

Requests符合所有相关的规范和RFC，这样不会为用户造成不必要的困难。但这种对规范的考虑 导致一些行为对于不熟悉相关规范的人来说看似有点奇怪。

编码方式

当你收到一个响应时，Requests会猜测响应的编码方式，用于在你调用 Response.text方法时 对响应进行解码。Requests首先在HTTP头部检测是否存在指定的编码方式，如果不存在，则会使用 charade 来尝试猜测编码方式。

只有当HTTP头部不存在明确指定的字符集，并且 Content-Type 头部字段包含 text 值之时， Requests才不去猜测编码方式。

在这种情况下， RFC 2616 指定默认字符集 必须是 ISO-8859-1 。Requests遵从这一规范。如果你需要一种不同的编码方式，你可以手动设置 Response.encoding 属性，或使用原始的 Response.content 。

HTTP动词

Requests提供了几乎所有HTTP动词的功能：GET，OPTIONS， HEAD，POST，PUT，PATCH和DELETE。 以下内容为使用Requests中的这些动词以及Github API提供了详细示例。

我将从最常使用的动词GET开始。HTTP GET是一个幂等的方法，从给定的URL返回一个资源。因而， 当你试图从一个web位置获取数据之时，你应该使用这个动词。一个使用示例是尝试从Github上获取 关于一个特定commit的信息。假设我们想获取Requests的commit a050faf 的信息。我们可以 这样去做:

>>> import requests 
>>> r = requests.get('https://api.github.com/repos/kennethreitz/requests/git/commits/a050faf084662f3a352dd1a941f2c7c9f886d4ad')

我们应该确认Github是否正确响应。如果正确响应，我们想弄清响应内容是什么类型的。像这样去做:

>>> if (r.status_code == requests.codes.ok): 
...  print r.headers['content-type'] 
... 
application/json; charset=utf-8

可见，GitHub返回了JSON数据，非常好，这样就可以使用 r.json 方法把这个返回的数据解析成Python对象。

>>> commit_data = r.json() 
>>> print commit_data.keys() 
[u'committer', u'author', u'url', u'tree', u'sha', u'parents', u'message'] 
>>> print commit_data[u'committer'] 
{u'date': u'2012-05-10T11:10:50-07:00', u'email': u'[email protected]', u'name': u'Kenneth Reitz'} 
>>> print commit_data[u'message'] 
makin' history

到目前为止，一切都非常简单。嗯，我们来研究一下GitHub的API。我们可以去看看文档， 但如果使用Requests来研究也许会更有意思一点。我们可以借助Requests的OPTIONS动词来看看我们刚使用过的url 支持哪些HTTP方法。

>>> verbs = requests.options(r.url) 
>>> verbs.status_code 
500

额，这是怎么回事？毫无帮助嘛！原来GitHub，与许多API提供方一样，实际上并未实现OPTIONS方法。 这是一个恼人的疏忽，但没关系，那我们可以使用枯燥的文档。然而，如果GitHub正确实现了OPTIONS， 那么服务器应该在响应头中返回允许用户使用的HTTP方法，例如

>>> verbs = requests.options('http://a-good-website.com/api/cats') 
>>> print verbs.headers['allow'] 
GET,HEAD,POST,OPTIONS

转而去查看文档，我们看到对于提交信息，另一个允许的方法是POST，它会创建一个新的提交。 由于我们正在使用Requests代码库，我们应尽可能避免对它发送笨拙的POST。作为替代，我们来 玩玩GitHub的Issue特性。

本篇文档是回应Issue #482而添加的。鉴于该问题已经存在，我们就以它为例。先获取它。

>>> r = requests.get('https://api.github.com/repos/kennethreitz/requests/issues/482') 
>>> r.status_code 
200 
>>> issue = json.loads(r.text) 
>>> print issue[u'title'] 
Feature any http verb in docs 
>>> print issue[u'comments'] 
3

Cool，有3个评论。我们来看一下最后一个评论。

>>> r = requests.get(r.url + u'/comments') 
>>> r.status_code 
200 
>>> comments = r.json() 
>>> print comments[0].keys() 
[u'body', u'url', u'created_at', u'updated_at', u'user', u'id'] 
>>> print comments[2][u'body'] 
Probably in the "advanced" section

嗯，那看起来似乎是个愚蠢之处。我们发表个评论来告诉这个评论者他自己的愚蠢。那么，这个评论者是谁呢？

>>> print comments[2][u'user'][u'login'] 
kennethreitz

好，我们来告诉这个叫肯尼思的家伙，这个例子应该放在快速上手指南中。根据GitHub API文档， 其方法是POST到该话题。我们来试试看。

>>> body = json.dumps({u"body": u"Sounds great! I'll get right on it!"}) 
>>> url = u"https://api.github.com/repos/kennethreitz/requests/issues/482/comments" 
>>> r = requests.post(url=url, data=body) 
>>> r.status_code 
404

额，这有点古怪哈。可能我们需要验证身份。那就有点纠结了，对吧？不对。Requests简化了多种身份验证形式的使用， 包括非常常见的Basic Auth。

>>> from requests.auth import HTTPBasicAuth 
>>> auth = HTTPBasicAuth('[email protected]', 'not_a_real_password') 
>>> r = requests.post(url=url, data=body, auth=auth) 
>>> r.status_code 
201 
>>> content = r.json() 
>>> print(content[u'body']) 
Sounds great! I'll get right on it.

精彩！噢，不！我原本是想说等我一会，因为我得去喂一下我的猫。如果我能够编辑这条评论那就好了！ 幸运的是，GitHub允许我们使用另一个HTTP动词，PATCH，来编辑评论。我们来试试。

>>> print(content[u"id"]) 
5804413 
>>> body = json.dumps({u"body": u"Sounds great! I'll get right on it once I feed my cat."}) 
>>> url = u"https://api.github.com/repos/kennethreitz/requests/issues/comments/5804413" 
>>> r = requests.patch(url=url, data=body, auth=auth) 
>>> r.status_code 
200

非常好。现在，我们来折磨一下这个叫肯尼思的家伙，我决定要让他急得团团转，也不告诉他是我在捣蛋。 这意味着我想删除这条评论。GitHub允许我们使用完全名副其实的DELETE方法来删除评论。我们来清除该评论。

>>> r = requests.delete(url=url, auth=auth) 
>>> r.status_code 
204 
>>> r.headers['status'] 
'204 No Content'

很好。不见了。最后一件我想知道的事情是我已经使用了多少限额（ratelimit）。查查看，GitHub在响应头部发送这个信息， 因此不必下载整个网页，我将使用一个HEAD请求来获取响应头。

>>> r = requests.head(url=url, auth=auth) 
>>> print r.headers 
... 
'x-ratelimit-remaining': '4995' 
'x-ratelimit-limit': '5000' 
...

很好。是时候写个Python程序以各种刺激的方式滥用GitHub的API，还可以使用4995次呢。

响应头链接字段

许多HTTP API都有响应头链接字段的特性，它们使得API能够更好地自我描述和自我显露。

GitHub在API中为 分页 使用这些特性，例如:

>>> url = 'https://api.github.com/users/kennethreitz/repos?page=1&per_page=10' 
>>> r = requests.head(url=url) 
>>> r.headers['link'] '<https://api.github.com/users/kennethreitz/repos?page=2&per_page=10>; rel="next", <https://api.github.com/users/kennethreitz/repos?page=6&per_page=10>; rel="last"'

Requests会自动解析这些响应头链接字段，并使得它们非常易于使用:

>>> r.links["next"] 
{'url': 'https://api.github.com/users/kennethreitz/repos?page=2&per_page=10', 'rel': 'next'} 
>>> r.links["last"] 
{'url': 'https://api.github.com/users/kennethreitz/repos?page=7&per_page=10', 'rel': 'last'}

Transport Adapters

As of v1.0.0, Requests has moved to a modular internal design. Part of the reason this was done was to implement Transport Adapters, originally described here. Transport Adapters provide a mechanism to define interaction methods for an HTTP service. In particular, they allow you to apply per-service configuration.

Requests ships with a single Transport Adapter, the HTTPAdapter. This adapter provides the default Requests interaction with HTTP and HTTPS using the powerfulurllib3 library. Whenever a Requests Session is initialized, one of these is attached to the Session object for HTTP, and one for HTTPS.

Requests enables users to create and use their own Transport Adapters that provide specific functionality. Once created, a Transport Adapter can be mounted to a Session object, along with an indication of which web services it should apply to.

>>> s = requests.Session() 
>>> s.mount('http://www.github.com', MyAdapter())

The mount call registers a specific instance of a Transport Adapter to a prefix. Once mounted, any HTTP request made using that session whose URL starts with the given prefix will use the given Transport Adapter.

Many of the details of implementing a Transport Adapter are beyond the scope of this documentation, but take a look at the next example for a simple SSL use- case. For more than that, you might look at subclassing requests.adapters.BaseAdapter.

Example: Specific SSL Version

The Requests team has made a specific choice to use whatever SSL version is default in the underlying library (urllib3). Normally this is fine, but from time to time, you might find yourself needing to connect to a service-endpoint that uses a version that isn’t compatible with the default.

You can use Transport Adapters for this by taking most of the existing implementation of HTTPAdapter, and adding a parameter ssl_version that gets passed-through tourllib3. We’ll make a TA that instructs the library to use SSLv3:

import ssl from requests.adapters 
import HTTPAdapter from requests.packages.urllib3.poolmanager 
import PoolManager 
class Ssl3HttpAdapter(HTTPAdapter): 
""""Transport adapter" that allows us to use SSLv3.""" 
   def init_poolmanager(self, connections, maxsize, block=False): 
      self.poolmanager = PoolManager(num_pools=connections, maxsize=maxsize, block=block, ssl_version=ssl.PROTOCOL_SSLv3)

Blocking Or Non-Blocking?

With the default Transport Adapter in place, Requests does not provide any kind of non-blocking IO. The Response.content property will block until the entire response has been downloaded. If you require more granularity, the streaming features of the library (see 流式请求) allow you to retrieve smaller quantities of the response at a time. However, these calls will still block.

If you are concerned about the use of blocking IO, there are lots of projects out there that combine Requests with one of Python’s asynchronicity frameworks. Two excellent examples are grequests and requests-futures.

Timeouts

Most requests to external servers should have a timeout attached, in case the server is not responding in a timely manner. Without a timeout, your code may hang for minutes or more.

The connect timeout is the number of seconds Requests will wait for your client to establish a connection to a remote machine (corresponding to the connect()) call on the socket. It’s a good practice to set connect timeouts to slightly larger than a multiple of 3, which is the default TCP packet retransmission window.

Once your client has connected to the server and sent the HTTP request, the readtimeout is the number of seconds the client will wait for the server to send a response. (Specifically, it’s the number of seconds that the client will wait between bytes sent from the server. In 99.9% of cases, this is the time before the server sends the first byte).

If you specify a single value for the timeout, like this:

r = requests.get('https://github.com', timeout=5)

The timeout value will be applied to both the connect and the read timeouts. Specify a tuple if you would like to set the values separately:

r = requests.get('https://github.com', timeout=(3.05, 27))

If the remote server is very slow, you can tell Requests to wait forever for a response, by passing None as a timeout value and then retrieving a cup of coffee.

r = requests.get('https://github.com', timeout=None)

CA Certificates

By default Requests bundles a set of root CAs that it trusts, sourced from the Mozilla trust store. However, these are only updated once for each Requests version. This means that if you pin a Requests version your certificates can become extremely out of date.

From Requests version 2.4.0 onwards, Requests will attempt to use certificates fromcertifi if it is present on the system. This allows for users to update their trusted certificates without having to change the code that runs on their system.

For the sake of security we recommend upgrading certifi frequently!